I don't see the difference between making that movie with a 15-year-old and making it with a 16-year-old. Both have already missed the window, imo.
If KA2 was gonna happen, it would have needed to start shooting last year at the latest. Unless, as you said, they want to tell a very different story with a high school Hit-Girl and college Kick-Ass, something they could still do a year or two from now. I'm just not sure who would want to do that.
What? The budget for Kick-Ass was a fraction of just about any other superhero movie, yet it's certainly better than most, with some of the best and most entertaining action sequences in the genre. Why are you acting like it somehow wasted its budget? I mean, its production values were at least on par with Daredevil's and that one had more than double the budget. The Green Hornet's budget was more than FOUR times higher than KA's. I'd say Vaughn's use of that $28mil budget was damned impressive.