Asking to create stages as awesome as Temple with all the 3D-ness and stuff would be far too much, of course.
Why would that be too much? Look, imagine the interface like this: You have a blank screen. You press a button and it brings up a panel with a list of categories on the right side of your screen. You see categories such as Backgrounds, Platforms, Actors, Textures, Events, and Music. Let's say you select Platforms. It now brings up a list of all the platforms in the game. You then pick one and simply drag it onto your blank screen. So say you drag some pokefloats into your level, and then maybe some Mario blocks in there, and then maybe you drag the entire Final Destination platform in for the base, and you want your level to be big so you grab two of em, so your level is now twice as long as FD, with pokefloats and Mario blocks in the sky, placed in strategic locations. Then you could pick whichever background you please, like the cool buildings from Fourside. And you could replace any textures you want. Don't like the texture on the FD platform? Change it to some cool DK wood, or maybe make it all clouds, like the one cloud in the Yoshi level. And say you want some cool hazards in your level. Click on Events, and it lists all of them, like rising lava, the Starwings shooting at you, F-Zero cars racing through, Kraid flipping the level over, etc.
You could also just open up an existing level and edit it. Like Temple for example, you could remove that whole platform at the bottom by just clicking on it and deleting it. And then add some more stuff to the top of the level to your liking; extra platforms, events, etc.
But the real lure would be making your own adventure mode levels. THAT would be sweet. If they implemented some sort of visual scripting language, (such as "Kismet" from Unreal Engine 3) then the possibilities would be vast. You could make your own long, side-scrolling level, with puzzles and bosses and hazards and everything.
This feature would definitely increase sales.
