I agree with the previous responses. In the next five years you will most likely see the tier system disappear entirely. With a soon to be announced huge expansion to DHS, there will be plenty of attractions to spread the FP+ choices around, and with the addition of a third screen at soarin, the Frozen ride, and the return of A&E meet and greet to Norway, Epcot will be just a few new attractions away from no longer needing tiers as well. I would be surprised if there are any tiers left by the time the 50th anniversary rolls around in 2021.