Civils Wars: Yes; Revival of Destroyed Factions: No; Time Periods: Absolutely

It was extremely aggravating in MTW to have a faction come back with far advanced units than they had before being conquered. Besides, the culture penalty forces a conquorer to garrison properly or rebellions will occur (not that rebellions are that hard to put down).

Civil Wars, on the other hand, would provide excitement because specific family members could take sides along with the cities in which they sit as governors.

Also, I agree that time periods wouldn't be difficult. It would allow Roman factions to go straight to the Marian Reforms. Plus, after a while I always played MTW in the Late Period so I wouldn't have to go several sessions of building and buidling before getting to the advanced units.