I would like a Engine like the Doom3 Engine... Look at those shadows, they would be perfect for lightsaber duels.
And everything what the quake3 engine can do, can doom3 do too.
I spend a lot of time in modifying the doom3 engine, and i must say, its one of the best engines i know, and the effects would be great.
Even a RPG system should be possible to implent, when you see Lineage2 got a Unreal engine, it means it should realy be possible, and why not? ^^
edit: and about the developers... Models can be used in every game. all they need is to write the main code for another engine, but that cant be so hard, when i see what they already did!