I agree with a vast majority of your post. I think that the only thing that has me a bit worried is the bolded above. I feel that a lot of the entertainment on Disney Channel is so "flash in the pan" that as soon as you built an area to showcase some of the teen-based shows, those shows / people would be already gone and moved along. Just think if they started building a Hanna Montana / Jonas Brothers attraction, they would be out of the public eye by the time they finished construction. It seems to me that even as it stands, with the Disney Jr. attraction, at least 1 of the shows highlighted is one that has already been moved out for other shows.
Now, if they wanted to get this demographic group and use the "Studios" part, I would think that an easy solution would be to move production of some/all of their live-action shows to DHS and let visitors be a part of the tapings, kind of a live-studio-audience. I think that this has been done in the past at the Universal parks (Maybe even at MGM, I can't remember as this was never something that would have interested me personally), but it could be a way to keep the working studio feel in DHS and keep the pre-teen folks entertained. I'm sure that logistically there is probably a reason that both Universal and DHS does not do something like this already, so I'm sure there are folks out there that can tell me why this wouldn't work. It's just the first thing I could think of where you could keep up with the fast paced change in teenage tastes, but still include part of the Disney Channel / Disney XD "brands" in DHS.