A rom hacker over on SMW Central is working on new Super Mario World rom hack starring both Celestia and Luna. It even comes with it's own specific storyline:
After the defeat of the Tantabus, the dream monster that Princess Luna created to give herself bad dreams every night to punish herself for the bad things she did in the past and that threatened to escape the Dream World and turn Equestria into a living nightmare, Princess Luna thought she could finally sleep peacefully, but it turns out that the Tantabus wasn't actually defeated. Parts of it escaped from the Dream World into the real world, and the parts have been giving ponies all over Equestria nightmares. Can Celestia and Luna venture across Equestria, destroy the Tantabus particles, and save everypony before it's too late?There will be 9 worlds in all, a star world, and a special world once it is complete. Right now he's built half of world 1.
You can find the thread for it over here.