The official
Terms and Conditions don't indicate that "day of" FP+ will be available. That said, they don't say they
won't be either. In fact, they are non-specific enough to allow for a wide variety of implementations -- and it's probably quite likely that a lot of specifics aren't decided or worked out yet.
Personally, I think the question of how "unreserved" FP+ slots are going to be allocated is a good question. It's quite possible they will just be left accessible only as part of a person's 3 per day FP+ numbers -- so that day guests can get some or people can change reservations on the fly or replace missed FP+ experiences. But it's also quite possible that the additional inventory might be made available for "day of" use or might be used to give Deluxe or Moderate guests extra passes or might be used for surprise "bonus" FP+ to manage crowds.
While I don't necessarily share @
dadddio optimism about FP+, I do think he correct that many people are taking the limited "facts" that we know and often extrapolated worse case scenarios and then condemning the system. It's one think to describe your apprehension and concerns, it's another to outright condemn a system that we don't fully understand at this point. I don't think it's that unreasonable to actually get some more specific and concrete details before we riot on Main Street. Just IMHO.