Great Ideas for more themes. I highly agree that all races should have SOME choices although we dont have to rush on that. It allows the game to grow staying ahead of player boredom. (boredom? Ive been playing Dom for 3 years. Oh well, you know what I mean)
Arco, well, I don't really have any bright ideas on that one yet. Maybe some great change comes about as a result of the astrologers seeing a great calamity and that empire changed in the resultant chaos.
Arcos seems to be the nation of choice for researchers. And it has always struck me as being also very strong in units. Pulling back on magic would take it toward the other nations which probably isnt needed.
Maybe a theme where it goes even further into research. Lots of variety in mages and sages and alchemists. But then make it so weak in units that it is FORCED to use independents alot. That would make it useful for people who want to play with magic. And useful for large-map games but probably suicide on small fast ones. It would be a niche.
Of course, someone could also mod these.
I think some really good mods should end up being adopted as themes. That would be nice.