A totally and completely impossible request (ive asked it before, doubt anyone actually read it):
Have an option or side-build specially for cutscenes. This would take the mission directly from FRED and play through it. However, the mission would have a seperate flag that identified the player as a camera and non-movable. The mission would play through as normal...BUT, you'd never see it. Instead, it would render each scene at a certain FPS and output it as part of an AVI. This will make it a true cutscene, and with it outputting each frame, FPS issues will vanish forever, although like another renderer, it would take time to finish the entire scene/mission in this case. But hell yes, it'd save a lot of trouble!