While not a huge fan of Aerosmith, I really hope WDI doesn't take some of the suggestions for replacement bands found here. Nickleback, Matchbox 20, Def Leppard, ELO, Linkin Park, The Cars?????? Are you people serious?? You want to replace a Hall of Fame act that has been around for nearly 4 decades with post-grunge crap rock, 80's hair bands, or new age??? Van Halen and Queen are the only suggestions that even remotely fit the current theme, or have more than two songs that a wide range of ages could even identify.
If Aerosmith does not renew its contract, I would much rather see (1) another hard/classic rock band to take it's place, or, (2) re-theme the ride to an exploration of rock and roll and the origins, influences, etc. The only real problem I could foresee is the licensing costs. For (1) a band like The Who, Queen, Rolling Stones, or more contemporary, Van Halen or maybe U2. OR for option (2) explore the influences and origins. Chuck Barry, Elvis, The Beatles. Now of course, to get some of these acts, or their music would probably cost Disney way more money than they would be willing to spend, but I think these would all be much better than any 'tween act.
To keep the ride's current theming to a "rock and roll" music coaster, they absolutely have to use a legendary, world-class rock and roll act. As many others have said, they would be seriously excluding a large portion of their customer base if themed to any of the 'tween acts. No way you would see a group of people without any children, over the age of say, 22, waiting in line to ride a JB, HM, or HSM ride.
I do not think Disney would make such a mistake. If anything, they would create an attraction based on one of the franchises that would be geared towards the target demographic, not re-theme an extremely popular attraction with a wide demographic to cater to the 'tweeners. And as EE said, they would get so many complaints about their daughter being too short to go on her favorites characters (yes Hannah Montana and her real-life counterpart, Miley Cyrus, are in fact face characters for the world to see) attraction.