Yer there is no point building MMF on top of another engine.
I like Nifflas's idea in his other post where he raised the idea that movements could be seperate so that people can program their own and can share/distribute it around the community.
And like other people have said before, people can still stick to MMF2 if they don't want to port thier games. MMF3 should be faster and built without backwards compatibility (except for the ability to keep artwork) so that it is as fast and optimized as possible.
And as long as it has LUA support I am happy