Cities and pioneers: In another post, I suggested the pioneer cost population because the city growing game isn't too interesting currently. There isn't much sacrifice in building hundreds of pioneers as it was in FE. My city grows and gets more powerful but it isn't very interesting compared to FE. One city builds exactly the same as another and there isn't any diversity. I'd suggest methods to diversify cities in four ways: production, mana/magic, sovereign (maybe logistics) points, and also crafting. Some examples:

Production city: better trained units with specialized buildings (much like FE)

Mana/Magic: Obviously there is no research for technology but a city specializing this would be cool. It would be the only one that builds essence buildings or more mana. One other special thing is maybe it allows for building that make spells more effective too.

Sovereign: to build up talent trees faster because after awhile I stopped needing more spells. This sacrifices production and magic of course but might give you more logistic or better pioneers or something to the effect.

Crafting: I think this would make an excellent city type because I don't normally have enough basic supplies to equip all my units. It'd be nice to have a city that specializes in providing continually source of crafting supplies.