first of all, I really appreciated Scirra and @Ashley efforts for pushing Construct2 with the best and important features, especially the functions support which added recently
here my top wishlists which will make Construct2 to became my first and only choice engine for my majority HTML5 games, if it's implemented, whether soon or later.
 Better Tile set Support :
I should admit i can workaround with this via gamemaker import somehow but i believe it will be very benefactor if Construct2 have better and easy Tilesets Support, similar to RpgMaker or GameMaker, it's a must for rabid developments, should be easy to change tiles and better visibility in the editor.
 Full object deactivation with event control support :
I read somewhere Construct2 ignore the instances graphics render automatically outside the view screen, how about to deactivate entire instances logic too from happening ? forgive me if this already can be achieved, but i didn't found it or know how to use with events system, in gamemaker if i deactivate objects outside view screen, not only graphics render part will affect but also the logic associated with it too as well, this helpful for better performances and better control for developers.
 Dialogue Objects :
If this officially implemented to Construct2 it will make my day, this really useful and important for RPG/Adventure/Visual Novels games, i tried to follow some directions to make my text dialogue it was hard ,complex and messy, all what is need is 4 arguments if it would implemented, to work very well in events system.
1- sprite box (the image size depend on the texts height/width).
2- text/messages: here we write the texts for the dialogue.
3- processed button: here to define the button key or var to define the skip process for the dialogue.
4- sub below events: wait/ignore ( if we put sub events, we can choose whether to wait all sub events below or ignore it, this for better control to not make all text messages visible from the starts or some middle logic from happening immediately before dialogue complete.
>>> notes: this should work in order lists automatically when add sub events to the dialogue event<<<
that's only my top wishlists for Construct2, i know some of the suggestions I listed can be achieved from developers side or usage of third parties plugins, but me personally like to work along with official features, to not worry about future compatibly/broken etc...
forgive me for my bad English. it's not my native language.