Nice list.
Fixing the AI is difficult since there is really only one. Do you feel its better for the AI if it never casts a spell which has already been cast? That would seem bad for spells like shards or fireball.
The problem with fortresses seems to be in the AI's budgeting. Alot of what people feel the AI should do (dispel globals, build castles, get more elite troops) would require shifting from a "best use of what I have" to a "save up for this" strategy. Plus the logic of castles is hard to figure. "A province I own which is surrounded by provinces I own and none of these provinces already have a castle". Does that feel workable?
Choice of targets? Do you mean that the AI should stop firing at anemy troops that are engaged with their own troops? Im not sure how that would be done to best improve overall combat scores. If the archers all shifted to rear enemies at that point then many of the shooter types would end up running forward thru the melee combat. The AI did switch to putting most of its archers on the flanks which helped alot.
The interface things look pretty good from what I see.
The themes and mods dont really apply. I get the impression that alot of the theme and mod stuff gets done because its fun.
Besides the person who would do most of the work on them is not the person who would do most of the work on the other stuff.