My #1 request would be a return to XP mapping. This includes:
Giving the player control over the layers
- allow layers to be edited separately, so placing something on the lowest layer doesn't wipe out what's on the layers above
- allow autotiles to be placed on higher layers
- allow the active layer to be viewed while others are dimmed
Make autotiles less "smart"
- don't change already-drawn autotiles when drawing next to them with a different autotile (this would be my biggest peeve with MV - and Ace and VX)
- bring back the autotile double-click function from XP - double-click on an autotile in the palette, to open a sheet of all 48 variations of that autotile, and select one manually from that list
- do away with shift-clicking, or have an option in the editor to use shift-clicking OR the double-click function above, so people can use whichever method they prefer
Don't really mind whether it sticks with the Ace tileset format or the XP tileset format.
And in the tileset tab, add the ability to reset flags on a tileset to the default (not all flags at once, but if you're looking at passage, allow all passage flags to be reset, and if you're looking at priority, allow all priority flags to be reset), and to copy flags from one tileset
slot to another (for example, if I want to make a dungeon tileset but have one tile slot from the indoor tileset, let me copy/paste the flags for that one slot/tab rather than have to do them all manually).
Allow for the engine to be modified.
This would be nice too, and if this could be done, it would probably be possible to do a lot of the other stuff people are requesting without having it baked into the engine.