[Suggestion] "Upgrade Magic School" as fixed level-up trait.

Exactly. I agree so much I modded this into my game. The likelihood of each spellbook is guaranteed and the different elements come at alternating levels. So you don't see 5 element choices in one level and 0 the next.

Why only magic?  It's just as unfair to not get any other perk if you're waiting for it.  That means you have to change all of them, or none of them, to be fair to less-magic characters.

Perhaps adding a rare perk "Upgrade of your choice" or "Magic upgrade of your choice" in addition to the current perks, rather than replacing them?

Because all the non-school perks in the world aren't going to matter if you never get to move off Fire Rank 1. And lower-magic characters rely on gear so much more than perks it's not even funny. But really, why only magic? Well, because the game is just supposed to be about magic, so why not? It's not the successor to Master of Less-Magic, it isn't the de facto sequel to War of Less-Magic, and it's not called Fallen Warrior. Magic can use some lovin.

The point is if 1 of the 5 is ALWAYS magic, there will ALWAYS be 4 other choices. I call that an improvement over current.

I would, however, like for the other 4 options to always be at least 1 of your class specialties. There are a lot of the general traits that are really underwhelming after the first level or two, and they tend to crop up a lot.

As to the OP:

Yes, yes, yes. I almost never use the Path of Mage, because it is the surest way to guarantee myself a wall of "Adventurer's Boon" and "Swordsman" traits at level up. We need to be able, for sure, to develop a caster (at least with our sovereign), because so much of the empire building is tied to magic. Having it be entirely random if you are even allowed to level up is a terrible way to approach it.

Agreed.  They fixed random techs because this annoyed the heck out of people in the tech tree.  The same annoyance applies to perk choices.  The "Path" system is essentially a weighting system that makes these random choices a little less random so you can specify character roles... but really, a perk tree (in other words, just letting us pick whatever we have the prereqs for) would just solve everything.  

The only problem with it is what if everyone kept picking the same choices over and over? Well, there's just not enough perk variability to avoid that right now anyways.  And, if people do that, that's a clue that maybe some of those perks are a bit too overpowered.  

YES, this I agree with.  We need finer control of our sovereign, but I think there has to be a level of randomness/chaos built in, or before long, lots of people will complain that everything/one is identical because an optimal build will be found.

I think a perk "tree" isn't quite the right way to tackle it, and I like the somewhat random nature of the non-magic perks. It's exciting to have that game where you get lucky and get a bunch of evoker levels, or double strike early on. I just don't think the magic system is benefitting from random rank upgrades.

At the same time, I'm all for random spell selection of the spells at a given rank, so go figure that out.

No problem

You get always a spellbook at a level up if you have selected that school at level 1, but every spellbook gives you only 1 - 2 spells of that level and you can select the same spellbook multiple times to get all spells like in MoM.

I'd like to see weighting for perks change based upon what you have taken before, which essentially comes down to a loose "tree" since you will be seeing the subsequent versions of traits more commonly once you have picked the parent.

Magic, on the other hand... This system is already a pretty weak magic system overall. I would hesitate to insert a likelihood that one of the truly 5 useful spells didn't happen at all. Now, if you are talking about having spells have "windows" that they can appear in either 2nd or 3rd level, I could get behind that. If you are talking about flat leaving things out, no. That would not be good at all.

If this system was implemented, wouldn't you have to rebalance the higher level spells to account for the fact that you could gain access to them very early?

In a word, no.  The spells are (or at least, should be) already balanced around the idea that you can acquire them at their earliest possible opportunity (which seems to be 2x-1, where x=spell rank).  The problem is, there's no guarantee that your archmage character will get ANY spell traits, let alone the trait they want, when they level.  Sean's idea sounds very interesting, though hopefully he added a couple traits to the mage path to make up for their decided lack of unique perks.  I also like the idea of having path of the mage simply upgrade all your spell levels at once in one perk: e.g., instead of choosing Fire 2, you get Magic 2, giving +1 to all your spell ranks.  How such a thing could be implemented, though, is beyond me.

Any one trait can add any number of other traits. I could do it, but I would never. When the Path mod part of my balance mod comes out, it will have traits that are super rare, but unlock say Water1 and Air1. You will have a .001% chance to find one of these as a mage.

yes to this idea but maybe limited to even, odd or divisible by 3 levels.

Upgrade magic option as described in the op shows up guaranteed on a schedule.  If you don't selected because of some rare trait pops up make it available at the next rank too, maybe.

I think that each class should get their main skill automatically uphraded on level-up in addition to the random perks you choose from. For example, a mage gains a rank in a school of magic every level. A defender gains ZOC and/or defense. A warrior gains +1 to the number of figures in a unit he can attack each turn (see my post about this). An assassin gains crit chance and multiplier. A governor gains %a bonuses to production, food, gildar when postes in a city. This way, the classes continue to improve in what theyre supposed to be good at.

I also think that after level 4, you should be guaranteed at least one trait from your chosen path.  In addition.  The RNG is a merciless god.