I could be wrong, but it seems like C2 is now at a turning point, features are working pretty nicely, the exporters aren't as big of an issue as before (mainly because alternatives to cocoonJS exists), it seems more like now is the time to improve what has been done and also improve the IDE itself.
My personnal suggestions:
-The image editor would like a little more work on it
-Even though I know it will not be done, the ability to change the framerate is still an important feature
-array and dictionnary behavior, as well as events sheets for the objects themselves rather than the layouts (not nessecary, but nothing is really needed when you think about it, it is just really helpful to have, and that could be a great help for new users)
-depreciating cocoonJS, and working on the functionnalities for ejecta, crosswalk, phonegap, also make the box2D physics engine uses it's full potential, since I think it is partially nerfed because of the cocoonJS physics engine, which is really not acceptable
-the arcade, right now it is just hurting this website!
-If possible, doing a node webkit fix for the problematics OS, I know it is not your job, but it is directly included inside C2 itself and on the front page of the site so it should work.
-theorycally an official wiki, could be nice to have, since forum topics can be lost in the crowd, and tutorial are not in the community edit spirit
-other things that this thread highlighted
-having the known issues listed inside the manual, I am not sure I have saw the family+container issue listed somewhere in the manual for example.
-I think the facebook plugin is not up to date.
Just suggestions of course.