How kind of you to ask; I apologize in advance for a lengthy post.
The first thing I realized (which I must have missed somehow) was that everyone would participate in FP+. Initially, I didn't see this as a problem, but then I hear resort guests get to pick their choices 180 days in advance. I don't plan my trips that far in advance and I still think deciding where I want to eat 6 months from now is insane. Anyways, if I want to get a FP+ for TSM, I'll probably have to get up at 7am 180 days in advance to book my package and get my FP+ reservation. Day guests get FP+ 60 days in advance.
Next, I didn't learn this from the podcast, but Disney seems that it is virtually eliminating the regular FP system. On average, I spend about 7 hours in the park on one day of a vacation. I could easily get at least 3 FPs for attractions of my choice if each return time is past 2 hours, which is only for select attractions. On average, I find that I usually get 5. These are for any participating attraction of my choice regardless of if I got a FP for it before, so I could get 2 FPs for Space, 1 FP for BTMRR, 1 FP for Space, and 1 FP for Buzz. Under FP+, I'd only be able to choose 2 of those attractions and not be able to ride one ride multiple times, and I don't get access to regular FP, so my only option is to wait in a long standby queue.
Finally, it's just too confusing. What if I have a FP+ for the MSEP but it thunderstorms (in the lightning capital of the world, mind you) and the parade is canceled? Seems like it would be a too bad moment, as I can't imagine many slots being available after the 11pm MSEP. I think the system could work if it was just offered to Disney Resort guests who could book them 60 days in advance and was used in conjunction with the regular FP system. That's how I initially pictured it.
It's worth noting that Jim Hill didn't seemed to thrilled about ti,