I hope you don't mind if I decompose your post, I think its better if I do it this way
Hotspot & image points for sprites
Yep. We need those urgently, especially if image points are unlimited. Also, a way to call "imagepoint<i>" via expressions would be nice.
Collision polygons so collisions are a bit better than bounding-box
Not really needed right now, most games can get by with collision rectangles or invisible detectors. The kind of game that would benefit the most from collision polygons takes more time to make (in my opinion) and would need a lot of features that C2 still doesn't have
Families (will take a long time)
Physics (not sure if Zack0Wack0 was working on this?)
If there's a chance he's working on it, it's better not to do it. Let the community work on it.
Support for the Chrome or Mozilla web app stores - it looks like you can even charge for web apps, so see if that's something that can be added.
Does that bring a lot of revenue? I guess the community can code plugins that work with those - besides, it's not urgent
Improved audio engine using Web Audio API (which currently only Chrome supports I think)
Let browsers mature? I don't know anything about audio APIs, so feel free to disregard my opinion here.
Good support for tilemaps
We're definitely going to need those.
Simple "fill color" on the image editor
Agreed, especially for quick recolors and knocking out transparency.
Also, I'd add a "rotate 90? clockwise" tool there too, as most top-down sprites are drawn facing up, not to the right (as construct 2 likes).