A Yoda movie sounds awful. So do most of the ideas I've heard surrounding these spin-offs.
Only truly solid idea for a film I've heard so far:
"Seven Samurai" with Jedi. Set a few years after RotS, Survivors of the purge (and friends) are gathered up by a grizzled, old, one-armed Mace Windu (going under an assumed name) who has been hunted down by a force-sensitive kid in the hopes of fending off the Imperial invasion of an outer-rim planet where the first inklings of a serious Rebellion has begun to form in earnest. An Alamo-esque finale (and death of these last few Jedi) kick-starts these beginnings of the Rebel Alliance.