Converting the assets to use the Spring engine (or BeyondAllReason's active fork of it) is probably easier than writing a new engine from scratch for the existing assets. And then it'll feel like BAR but with C&C's assets. The UI is what gives the game most of its feel.
C&C Generals plays completely different compared to Total Annihilation like games with streaming economy that Spring was built for. I like both subgenres of RTS, but they are very different.
With the game engine opensourced, I doubt thats true. Its probably going to be much easier to just get this code building (patching out any proprietary bits and pieces) and going from there.
Modding the game to work properly at a high framerate doesn't sound very hard when you have the original assets & source code to work from.
