Would it be feasible to make factions evolve in some way?
-Slowly gain technology, either from the player or from other factions. This could also come with some kind of meeting (event) which you could influence by attacking to deny the technology to a tribal enemy or to steal it.
-Also, factions may chose to settle near you (creating a new settlement), forcing you to raid them and raze it.
I like to begin my game with primitive weapons only and then slowly progress to a more advance level. These games sometimes take me 10-15 game years (and many death pawns) to complete most of the research.
Also it would be good if you could reverse engineer weapons to try to gain points towards a technology.
And make technology more expensive.