in addition to the things mentioned above:
1) Real camera and 3d placing of the layers. I am not talking about obj or any kind of 3d mesh support, no, just a 3d world to place assets around, like in Toon Boom, or HitFilm software.
2) Per Layer and per Sprite masking options. The current webGL (?) Destination Over,Out and whatever, are hard to implement and have a counterproductive workflow. A system that uses either gray-scale maps, or opacity values to mask any number of layers or objects (using other layers and/or other Sprites) will be ideal.
3) A timeline on the editor, with key-frame capability, to visually time and move objects around, add/or trigger events. This...
4)...in combination with a curve-path editor for making paths ( attach object to a path, set speed, way-points, ping-pong behaviors etc).
1. you can use magicam plugin for a camera - which should be made official and comes with C2 by default. Not sure what you mean by 3d object placement. Isn't Z ordering what you ask for?
2. Sprite masking would be really nice. It could be done similar to how containers work. Add mask object for the sprite and it will affect only this sprite. Doing that with effects it's sometimes difficult and its forcing you to use separate layer.
3. This could be made but as a plugin because that kind of feature will simply not fit to current C2 workflow. But still, would be perfect for cutscenes and timed events. There was something like that in CC, Timeline? if I remember correctly.
4. I'm surprised C2 still lacks of path editor after all releases. I know it's quite easy to do by events, but proper plugin for that would be great.