Using the FP+ system as a guide, since I think that will be the technology that they are modifying for the new system (I work in IT Finance systems development, and understand the complexities of bringing up a new or modified system). Purely speculation, but my chips are obviously on resort guests getting access to the reservation system first, starting Day 1 of check in for length of stay (up to 7 days, similar to the FP+ system) with the added wrinkle of #days on ticket. So for instance, we have a 7 day DVC reservation but only 5 day park tickets, so I would expect to only be able to register for a park on 5 days. My guess is AP holders will be phased in early as well and allowed to hold 4 park reservations at a time BUT if they have a resort stay booked, then they would fall into the category above. This is very similar the FP+ rules, and I just don't think they have the time or IT resources to do something drastically different. They are most likely taking what they have and doing a copy and then modifying since a lot of the base coding is already there. I do think they will allow park hopping (maybe not immediately but shortly thereafter at least for AP holders), but it will be a standby type of thing, as people leave more can go in.