I had few ideas that I think would be good for the game in the long run. I'll list them below.
1: Versions of the current armors for both cold, warm, and temperate areas. I think heavy armor for example should have both a cold, and warm weather version, same for the light armor.
2: I also think it would be good for there to be a tunneling mechanic as well, make it to where you can dig into the ground, creating mines, and underground facilities.
3: It would also be interesting if there was a building option where you have buildings made from actual stone, and wood. I'm referring to buildings like what was found in Briton prior to the Roman's arriving.
4: I would also like to see additional siege weapons, like ballistae, scorpions(not the animal), and catapults. These would add more flexibility and options.
5: I would also like to see a option to form a army of thralls into things like actual armies, with formations, officers, and more. This would give a good RTS type aspect to the game, and make for larger and much more dynamic battles.
These are just a few of the ideas I have had so far. I'll post more as I think of them.