Some thoughts:
- A lot of features (per-pixel collision, tile-by-tile collision) that were well suited for the job in older days would be inefficient with hardware 2d rendering and a full-blown physics engine modeled after 3d physics.
- A lot of cool things (guiltless translucency and sprite scaling/rotation, efficient arbitrary convex hull physics) can be directly incorporated into features of the map editor. Like maybe we can specify a map's collision scheme using large polygons and such?
- This sort of editor could be useful for compiling some sort of sprite object thing (as specifying convex hulls for an arbitrary sprite by code can be tedious...)
- Tiles are cool. But then again, does it even need to be tiles?
- Possibility: You could specify a map file output with lua and directly include it in a game's source. In that case, you could even precompile it with luac...
- Heck you could write a map editor in LOVE, but that means working with the restricted file system subset.