I plan on working on a Super Mario World hack that can be ported to the Game Boy Advance under Super Mario Advance 2's remake of SMW. WhiteYoshiEgg already made a pure vanilla hack, but that was only 6 levels long. Mine is going to replace ALL of the levels, without making a custom overworld, title screen, or palletes. If you want a version with more custom stuff, I will make a later version of the hack with those added. Right now, I want to know what you guys think of the idea.
Your choice. It would definitely be interesting to see a hack being ported under SMA2's remake of Super Mario World; however, like MP said, you'd have to avoid using custom resources to make it fully vanilla and fall under the restrictions given. If you're going to make a hack like that, then good luck. I'd like to see how it will turn out in the future.