I've been looking into the xml a lot, and I've noted some key areas that I believe are possible to mod for a positive or expanded view of the game. Note, these are the things that are new to FE. There are many things that were possible in E:wom that still are in FE, but I won't mention them.
- The champion upgrade system is extremely sound, and practically limitless as long as we can keep things unique and interesting. The good thing about traits is that they can have prerequisites of any combination of unitstats, techs, and unitlevel. Of course, once you unleash the unitstats, you can practically do anything you want. For example, a magic sword can give you a hidden unitstat that allows you to later gain the trait bladesinger. A faction tech can allow you to gain new traits as well, or character backgrounds, or quests, or some debuff you happened to get in a fight, or injuries. Also, it's a little work but it's possible, each trait has a likelihood tag which is static, but because traits can be mutually exclusive we can dynamically increase the odds of a certain trait appearing by adding it twice or more (only risk is it appearing more than once).
- Speaking of injuries, unfortunately, they appear to be not at all so well implemented as traits (in terms of modding). They simply do not recognize either the prerequisite tag, or the likelihood tag. So, all we can really do to the injury system is add new ones and tweak their power.There is a potion that removes all injuries from a champion, so I guess it is only a matter of time before someone moves that function over to a spell.
- There is a fundamental game system open to modding when it comes to melee attacks. But we do not have access to the actual formula of attack vs defense. It's a lot to go into, but we can add new damagetypes such as blunt damage and so on and assign them to a certain defense, and create a %-resistance-unitstat as well. In addition, through hidden unitstats, we can create groups of units not directly obvious to the game - such as "Mounted - This unit counts as Mounted". We can then refer to this unitstat in bonuses. For example, it is a very small thing to make a special spear that deals 20% more damage against mounted units. Conversely, we can give mounted units a trait that allows them to deal special damage or defend themselves better against unmounted units. Mounted units is just an example, of course. We can also create other such groups, for example a set of weaponry that ignore shields on enemies, or specifically causes damage to magic armor but is weak against non-magical armor. Such things would take modding the items and/or units currently in-game. Really, anything that activates a unitstat can be used here - for example a trait that gives you +3 attack vs any enemy occupying a desert tile in strategic mode, or +3 if you are occupying a mountain tile. Also, the huge caveat here is the AI not knowing exactly how to use such mechanics.
- Speaking of the AI, it seems very keen on using custom unitdesigns and monsters and such. This is a vast improvement from E:wom. For unit designs, the AI seems capable of using the auto-upgrade system. Also, there are priority tags for magic items so the AI doesn't have to try to think how powerful a magic item is, we can just tell it.
- The spell system has many new neat features that are logical but were missing in E:wom. Most importantly, you may specify what casting the spell does to the caster, and the target, separately. In addition, we can specify what happens when a spell gets resisted. There's a lot of other neat possibilities as well, such as a "comet" spell that deals massive damage to one tile, and a lot less damage to those around. Also, we can specify if a spell stacks or not with itself.
- Speaking of spells, there's also a random spell in the game called Chaos, with a very interesting xml tag. I've only looked at it briefly, but it appears that we should be able to get item/unit procs working. Ie, when wearing this shield, anyone who attacks the wearer has a 20% of losing 5 dodge from a chill. There is a meleeappliesspell trigger, and a meleedefenseappliesspell trigger (which can also be used for non-procs obviously). There are some big limitations - you can only do one gamemodifier for the proc, it doesn't respect cooldown, it can't cost mana, and so on. Either way, in terms of increasing the variety of items this is great news. Also, I noticed there was a modifier for BattleAutoCastSpell, but I haven't tried it out. By the way, the random spell xml tag doesn't work in strategic mode currently, only in tactical mode.
- Wildlands seem possible to add. Also new sorts of terrains but only in coremods = bad idea in beta. Specifically, I'll be working on adding magma rivers, rivers of blood, poisoned river. I hate that every river is blue and cuddly.
- Cities also have a few new features in FE. Factions gain militia (which can be customized for factions btw), and buildings that summon defenders. Cities can also cast a defensive spell at the start of a tactical battle. Of course, there's the city level-up system for unique buildings (I haven't tested those out for prerequisites, but they are abilities like traits technically). Also, buildings that unlock local items. We should be able to add whole new types of functions like materials and grain, but I haven't tested that at all. Also, buildings can relate to their materials and grain in various ways. And then there's the obvious additions of buildings being able to add traits to trained units, or stats to defending units.
- One huge change from E:wom is the background handling of tile graphics and item art, but I haven't really been able to test those out yet since the workshop is locked. It looks like it will be very useful for adding new complete "factions" like another type of Kingdom. Also, I may be wrong, but it appears a specific tile can have different looks depending on the underlying terrain. Of course, cities are always cities but for world resources or even goodiehuts it may be interesting.
One thing I've noticed in regards to the spells is that every spell does something different. That's really impressive, in my opinion. There are not two spells in the game that deal damage in the same way, or give buffs/debuffs that are the same.