I agree the concept is possible - FPS creator is a move in that direction. I haven't tried it so I can't comment much, but I (possibly unfairly) presume it's very drag-and-drop and not particularly flexible (eg. could you make nonlinear games loading sections of a world at a time like Crysis? could you make driving games and aircraft flying games? other 3D games like a 3D RTS or 3D simcity type thing?). As in, it's basically a heavily moddable FPS game with a limited engine. Now I don't actually know anything about its engine and I'm operating purely on stereotype (I'll try it out some time properly), does anyone know if I'm right or wrong there?
My idea with Construct was not to make it 'Platform creator' or 'RTS creator', but be good in all areas of 2D, which is the most useful way to make it. Even if I added features specific to a genre (originally containers were designed to help create a unit for an RTS game) they were deliberately generalised to be useful to any type of game. So if I made a 3D game creator, I'd instinctively want it to be able to do all those 3D styles. As you can imagine... that's quite an engine to embark on.