Here's my question regarding making reservations for trips booked in 2021, isn't Disney saying that you can't change park reservations once they are made? Assuming the park reservation system stays in place, but things are better with COVID by then and Disney has more capacity, wouldn't booking on Monday for those trips potentially put you at a disadvantage should hours change and more slots open up? I would be annoyed if I made an 11 AM reservation at EP (aka first timeslot) for a Spring 2021 trip only to find out that the park hours were shifted earlier and I couldn't modify.
I wonder if it would make more sense to hold off on 2021 park reservations for a bit until you get closer in. It's not like they are going to run out of 2021 reservations on Monday or anytime soon even if capacity is kept at what it is for the July opening. This is also why it boggles my mind that Disney isn't doing park reservations on a rolling basis of like 30-60 days prior to arrival. Not only would it limit the number of people trying to make reservations on Monday, but it would also give them more flexibility to tweak the system as things change with COVID and they have a chance to see how it works in action. Not to mention that it could give them a way to preserve a preferred booking window advantage to on-site guests and market that as a perk for staying on-site. If they really are allowing 2021 park reservations, anyone who books a trip between whenever that opens up again and September 29, 2021 will lose the on-site advantage after June 28, 2020.
In the end I don't think it will matter all that much for park reservations in 2021, since they aren't going to run out for a while on those (there just aren't enough people with tickets and reservations for that to be the case, even factoring in AP holders), but it just seems wild to me that Disney would make things more taxing on their IT and potentially more frustrating for guests when they didn't have to.