I have my own theories, but curious to hear what you thought?
I was thinking that message was as much about letting people know that even if they book a reservation after 7/1 some of those reservations as well as some existing reservations will need to be cancelled or changed once things open. For example, if restaurants are open at 50% capacity (and some don’t open at all) lots of ADRs will be impacted. If the resorts open at 50% capacity (and some don’t open at all) they will need to move people around and/or cancel their reservations. If the parks open at lower capacity and have a reservation system put in AP holders may be restricted or blocked completely, multi-day passes could be forced to convert to single day tickets, resort guests may get first crack at time slots for parks. That kind of stuff.
I do wonder if due to the Universal announcement there was a surge of WDW booking for the beginning of July anticipating the parks would definitely be open. If there’s changes to any reservations I would assume the priority would be based on time booked so the newest reservations would be cancelled first. In other words I wonder if they were setting the expectation that if you rush to book in July right now don’t be shocked if your reservation gets modified or cancelled.