Or there's a hybrid approach of just adding a couple of SSDs to the existing design without touching the three 3.5" HDD bays - - wouldn't be a bad thing for Apple to OEM at least the boot drive this way to then be able to lay claim to those I/O performance gains.
While a couple of 2.5" bays replacing the second optical bay is one approach (and a popular aftermarket mod), another alternative would be to put a fast "boot" SSD right on the motherboard by using the same "SSD Sticks" that the MacBook Air is already using.
-hh