This isn't the first time SolidSnake11 has found unused content in Dino Crisis. In this case, he found the SMB theme in the Japan only DC2 Trial Version. It sounds like it was a test of some sort (Not exactly an uncommon thing to do in gaming). But this being there is quite the surprise all the same. It's always neat to see new secrets being uncovered even all these years later.
We now have all we need to get Regina in Smash.