This is turning into a mod. Any ideas I have that aren't in the devs vision become mods. 

I am starting to notice that the flaw in this sort of class system is that when you get past the last class, you are basically going to only get random options or will be forced into cross-classing. I think making prestige classes is a good way to keep levels moving along. My goal will be have a trait system that can't me maxed out for thousands of turns. It will be simple to just keep updating the mod with more and more prestige classes and continuing the final classes to much higher levels. I also am thinking that every class trait you decline will have to pop up again each level. I will have to figure a way around this. I want you to be able to get them again, but if you chose random a few times in a row it would obscure the random traits. 

I love this idea, both from a lore perspective, and as a way to specialize heroes (I love specialization). I hope the devs a good look at this.

If you reach the end of a branch, that obviously means your hero is strong and has survived a long time. Why not let them just choose another branch at that point? That way you never reach the end. That would seem to be the easiest way to let them be infinite.

It's hard to balance these classes with no info on the final hero balance. I would need a time machine. But I like the idea that you start with vague ideas of a class and then specialize it over the course of the game. As you move on, each new specialization focuses on two stats that will further specialize your character. In the two levels of each class, you can choose some interesting bonuses and abilities. What I would like to do is have per level bonuses be more like D&D, where you don't get it every level, but when you do it matters. 

I am trying to create counters for the later classes and make each class a counterweight to specific strategies. Barbarians can wipe out large grouped units, Assassins can prevent heroes from acting and so on. I also want to control how much Initiative units can get. We may have some balance to this at some point, but Initiative is the quickest way to break this game. 

A more modular system is the best way to do this. I updated the link in the OP. Also click here. 

If you can get a good fairly balanced and filled in path trait list with a middle beta version, there might be even a chance the devs will use it.  I hope so! (pretty much all the work would have been done! )

Lots and lots of good thought here. I really hope that a great deal of this gets incorporated into development, as I too find that the traits are a key part of a fun experience.

One distinction to make is between traits that are mutually exclusive and traits that are not, but are so related to each other that they make for redundant options at any one opportunity to choose. So, for example, I don't particularly have a problem with the Assassin path having multiple traits that improve dexterity (eg. "dexterity", "grace", "quick", etc), some of which have added benefits and are more rare. But what is completely redundant is presenting me with more than one of those at the same time. There is no choice between +3 dex and +3 dex/+1 init - I'll pick the better one every time. More to the point, this redundant 'choice' takes up a slot that could be used for another trait that would present a real choice to consider.

More generally, I agree that "The Path of [Class] traits are the best traits one can get. Granted these are rare and granted you generally only get two per hero by level 15. But the problem is that these traits don't feel connected enough to the traits they unlock." Certainly, refined options and a better underlying mechanic will go a long way to solving the problem (as per your suggestions). However, I think even better graphic design/UI could help. Right now the trait choices are presented in a generic format, and the 'badges' that you get on your character identifying traits are generic. There's nothing visual to tie the traits to any one path. There are all sorts of ways to visually organize skills/stats/traits - see pretty much any other game that has such a progression, from any genre (Skyrim, League of Legends, etc). A common example is a progression tree to unlock (even Civ V had this for civ traits), although that's not the only way to do it. But please - pick something! Undifferentiated paths are confusing and not as interesting as they could be. Heck, from an RPG perspective, that's one of the key ways to build the story of your character. FE is big on incorporating lore and story, why is this opportunity being missed?

@Tasunke, 

I think the very term Assassin should be a high level path. Many people seem to be more comfortable calling it Thief or Rogue. Rogue is a good general term I think. I would like to see this changed, but until then, my mod will try not to change the core game. So whatever the core Paths are will be where I start from. I see no reason not to add a low level Path of the Rogue parallel to the basic Paths though. In my mod each Path will have a primary stat and a secondary stat. I can't be more specific until we get closer to the release version. It isn't necessary to nail down 3 or 4 Paths to start from. There will be many more than that. How about thinking of some new Paths I haven't thought of yet to help out this mod? There are, as you can see in the chart, many Paths that don't go anywhere yet.

You have some good ideas there. I will try to think of ways to implement them. Backstab is impossible in this game. That is just something we have to live with. I decided to take the idea of backstab and turn it into something usable: Critical Strike: Guaranteed Crit, +50% critical damage. So the idea that roguish heroes can use the element of surprise is held intact, without needing directional attack, which this game can't do. I hope they come through with the new beta next week so that people such as yourself can start to learn the new game and work within its limits. You have alot of ideas.

I don't have a critical skill 2. I would likely make this ability only usable once per battle or perhaps once every 6 turns. A guaranteed critical ability in the game implies that it will always hit. The strike is not seen by the defender and thus cannot be avoided. This would be a rare ability only unlocked at high levels. It would be a reward to a high level unit. Some things can be balanced by making them hard to achieve. 

I renamed Assassin to Rogue in the chart I made that is linked in the OP. +1 Dexterity per 2 levels and +2 to Crit chance per 3 levels, as well as +25% to crit damage. The Assassin has a very low attack so I want to make its crits common and powerful. A crit goes straight through armor, making it a valid choice on the battlefield. Their weakness is low health and low strength, making them easily encumbered and have low attack damage. So their attacks either crit and ignore armor, or don't crit and are totally absorbed by armor.

That is just the design for the Path. As you level you will get some accuracy bonuses and will get Dodge to compensate for lack of armor. Once the new beta is out I will make a few demonstrations on livestream and post the links here. 

Once you get to higher levels, there will be new Paths that further develop your hero. 

After much discussion about kiting in a different thread, I am going to have to make a list come beta 2 of battle tactics and counters. Then I will allow each Path to counter some of those tactics. The biggest worry is that the AI will not be able to use my counters if they require the purchase of specific weapons. I am also not sure how it will counter any tactic I use in battle if my units are multipurposed. Alot is riding on the AI being smart enough to counter things. Frogboy has indicated that he will only be able to justify spending more time on the AI after release if FE is well received. I suppose I feel the same way about this mod. What is the point of an in depth leveling system if no one ever uses it? Hopefully we have a good launch and a good 1.0 AI to make these ideas useful.

But in good faith I will continue with some basic countering ideas:

Path of the Assassin: A roguish hero that specializes in befouling enemy tactics. The Assassin relies on flawless accuracy to execute his mischievous bag of tricks. He is expert at ranged combat, relying  on critical strikes to seriously wound his foes. When he cannot outright kill an enemy, he prefers to counter their tactics against other units. Even the most rapacious mounted archers can be thwarted with the Assassin's expert use of tripping devices, poisons, drugs, and exotic weapons. Though the Assassin is a powerful tactical ally, his greatest weakness is lack of health and armor, instead relying on reflexes to avoid attacks. Neither is he particularly resistant to magic. 

Abilities:

Trip: Target is knocked prone.

Poison Dart: Short range dart poisons target for 4 damage per turn.

Smoke Bomb: All units in a radius of 2 gain 5 dodge and 10 Air Dodge, -75% to Accuracy. 

Flash Bomb: Stuns all units in a radius of 1.

Drug: Causes target to have a 50% chance of striking the wrong target or himself.

Net: Causes target to lose all movement with a 50% chance to lose 10 Initiative for one round.

Explosive: Causes an ear shattering explosion. All units in a radius of 1 take Piercing Damage and are knocked prone. Mounted units have a 20% chance to lose 4 Initiative. All units in a radius of 2 lose 2 Initiative.

Bolas: Target has a chance to be knocked prone and lose 10 Initiative each round for 3 rounds or until the target resists. 

These are only a rough draft of how I will likely add to the Assassin's Path. Assassin's Creed, oddly enough is a great source of inspiration for this Path. Also the Batman. These are all abilities I can certainly make. The uncertain part is the AI using them correctly. For instance, Smoke Bombs can be used on the enemy to blind them or on my own units to protect them. Furthermore, how will the AI be able to choose form a range of abilities? That will be the limit of this kind of mod since I don't think modding will be possible in multiplayer. 

I thought about that, but I eventually realized that any trait like that would be obsolete with the current Accuracy system. If Accuracy is going to increase with level for heroes, so will the Assassin's Dodge. The Assassin's Accuracy will also increase much faster than other Paths and will thus be able to attack in smoke against weaker units. Many Assassins will use bows, so I don't want to penalize them for that. 

Playing Counterstrike: Source, I learned how to aim at something mentally before the smoke was thrown and could get headshots with ease. I am going to assume these Assassins are almost as good as me.