make cities/castles/villages more upradable (ex. villages can have a palisade built...)
I have a very similar idea for a mod like that, but I dare not to post it on this forum coz it's a "if you want it, do it yourself"-world out there ;P and I cant mod, just make up awesome ideas *cough cough* Well, it included upgrading your village with loads of stuff, one was a smaller wooden fort where you could garrison troops to hold off enemy raiding parties.
Other than that, this mod would be awesome!

I like the Saxons and the Vikings (they were related) I'm gonna kick some Norman ass with the help of them!
With a mod that takes place earlier, I meant to include factions like the Picts or Britons or Iceni or Celts or Gaels or something. Of course some belong to different eras, like Celts were after Iceni and Britons, and I don't even think Saxons were around in Brittania by then. The Romans were, so that would be hard for you to make them (since you cant use any native stuff for them.)