But that's exactly how it worked with paper fp, headliners were gone by mid afternoon most days at every park, but we park hopped successfully. I think most people who hop get in multiple visits to each park. For instance, we'd got to the MK for our morning park, then hop to HS for the evening after a break. On that day, we'd get paper FP's for headliners at the MK, ride secondary rides at HS, getting any available FP's and getting FP's for shows that never sold out until very late. Then on another day, we reversed it. You don't have to have headliners available in the evening if you hop because you can alternate park mornings and evenings.
I much preferred FP+ because we could ride secondary rides at our morning park and then schedule FP's for the evening park, but both systems worked.
We just won't know until they actually put out more details, but I would be beyond shocked if they held back availability and people who were in the parks during the morning and early afternoon weren't able to ride headliners while people in the evening could. That said, I've been shocked before. I do think they're going to have a problem in that people seem to think that just because they paid $15, they are somehow guaranteed the ability to ride whatever they want- and that's just not going to be the case no matter how they do it. They are going to run out of LL reservations or the LL is going to be slow and jam packed.