But in terms of the actual implementation of enforcing FP return times, there wasn't any infrastructure change. It just merely required the CM's to alert everyone (and thus grow some pretty strong backbones to listen to the inevitable arguments that were going to ensue). So starting it in a heavily traveled time didn't need much.
This is a HUGE change. Installation of the new RFID readers, issuing the bracelets, putting out the technology to advance book (which as we have seen just in the initial roll out of the basic My Disney Experience has been a nightmare) and more.
Even if Jim Hill is right (is he ever?

J/K) that they start this at BWI next month, I still think there will be too many kinks to work out (or as Robo says, it will need more fixes to fix the fix) that it won't be going resort wide by then end of March/early April (ie peak Sprink Break crowds).
But that gives them the rest of April and all of May, somewhat lower season, to tweak and continue rolling out in time for the big summer crowds that start right around Memorial Day.