I just beat this game, and I don't want it to ever end! This game has PLENTY of modding potential, from custom levels, graphics, mechanics, playable characters, gimmicks, etc. I hope it happens one day! A source code would be even better!
We're looking into making an official level editor in the future, but I don't think we'll ever have official mod support. That said, I know a number of people are looking into doing game modding themselves.