Thunderbolt and USB3 seems to be overkill, it would make more sense to stay with USB 2 because that would make the components cheaper. USB 2 for peripherals that don't require too much in the way of transferring information and Thunderbolt for the heavy lifting.
The MBP would benefit more from Apple going to an SSD standard than from adopting USB 3.0. That would be an investment that would benefit the user base the most, as thunderbolt is that much better than USB 3 to begin with.
USB 3.0 is already integrated into the new Ivy Bridge processor framework. Moving back to 2.0 would be pointless.