It's absolutely possible to make a "real" mobile game on construct2.
But it requires a great deal of skill right now we are in this position:
PhoneGap. Possible with a more than average knowledge of obj-c. My new game (that I'm deciding about publishing it with cocoon or PG) is a simple puzzle game (but not static, think tetris) with more than 80 sprites on screen (all moving) and I get around 40fps constant. On my iPhone4 the cpu goes to 99% constant though and that's the only reason for moving away from PhoneGap. Possible? Yes! Hard? Yes.
To achieve this I optimized both the C2 engine and PG as well, and I can't publish the modification because are made specifically for my game. With the amount of effort I put into making it work I could've easily done it in obj-c.
Sadly PhoneGap is not ideal for making games, but has the advantage of supporting Game Center and all the plugins for Construct2. But, and I want to stress this, it's possible to publish games with PhoneGap.
CocconJS. I think that the support that C2 is currently offering is lacking, but this is the way to go. My game runs at constant 60fps with minimal cpu use. The issue here is the lack of a "Game Center solution" and support for anything else plugin wise. But with cocoon it's possible to publish full fledged games with tons of moving sprites and effects.