1) Cross Platform. This is probably the most important thing - Bring Construct games to as many platforms as possible. Pc, Mac, Linux, X360, PSN, Wii, iPhone, Android, you name it.
2) Make it possible to share game mechanics in a simpler way - If I have a double jump group that is all setup and works, it'd be awesome if we could take that group and just drag it over to another project and - boom - I have the double jump mechanic in my new project.
That could be amazing with mechanics that we could share online - One guy figures out this really smart way to create split screens and everybody can just take that resource and bring it into his own project.
Isn't flixel working like that already? This could make Construct soooo powerful.
Actually, if those two things can be tackled, I'd be one happy donut.