Crowding has certainly become an issue in WDW, despite their larger walkways. It's particularly troublesome near the FP returns, which tend to get backed up. Unlike DL's existing system where a group can hand their stack of FPs to a CM who glances at the time and accepts them, each person has to scan their FP individually. This process can take a few seconds per person (I'm sure it will be even slower when dealing with barcodes and a wide range of devices), causing dozens of people to spill out into the walkways. Given how cramped DLR already is, especially in places like Fantasyland where there's just no space for an additional return queue, I'm fascinated to see how this will work out.
It's also completely rearranged how people move through the parks, and which areas are the busiest. I'm sure there are ways to tweak this based on FP allocations and return times, but there are so few places in DL to wait 5-10 minutes for your time to come up that I'm sure there will be new bottlenecks that never existed before
Overall I actually think the MM+ system is pretty helpful (though most WDW parks don't have enough attractions to justify it), but I can't wait to see all the hand wringing by the APs who are terrified of any change, especially one that comes from the dreaded east coast!
