If I could really choose a medium/long-time project for you
, then it would be a full-blown L2 editor, with support for the various objects and good playtesting (fast startup of the game).
lgl2 isn't free nor open-source, it's Windows-only, and has usability issues (hotkeys). PCL2ed is rather hard to use, according to geoo at least -- I haven't tried it much, and I don't know what it can or cannot do. I think neither of them supports all the objects. geoo's L2 suite ties all of this together in a loose, but usable manner.
As said earlier, if you'd like to hack Revolution, go for it! It's just that I won't use a Revolution editor much -- I didn't check whether the game runs in Wine at all, and never built many levels in the existing editors for other games either, despite highly valuing their availability. (The Lix editor is the only one I know how to use properly, but the vast majority of Lix levels is done by Rubix, Clam, and geoo!)
maybe a better way to go is to enhance Lix to support the objects in Revolution
Hmm, this is sounds daunting >_> For multiplayer at least, different gravities do not enhance the game at all, this is my experience with Clones 1v1. Switches, retractable walls, and all this good stuff require a much more elaborate format for interactive objects than I have right now. There is actually a small demand for a better format even now, but it's not a short-term goal...
-- Simon