Played CoE2 recently and loved the concept and playstyle. It could do with a massive makeover and include stuff from Dom3 like forging and more advanced battles (but not like Dom3 IMO). I'd love for SP if the battles were in the style of Master of Magic but know for MP this is not good.
The ability to build roads to improve movement (with different leaders capable of different quality roads) would be good, along with the ability to "upgrade" map components like towns (by building a marketplace to improve gold income) or forests (via magic to improve fungus and improve fire resistance).
I'd buy it.