Keep in mind, with the reservation system for APs, they can easily cap how many APs are allowed in just like they did before. They may only allow 30% of the attendance for the day be APs and if the park isn't sold out, maybe open it back up on the day of for APs looking for last minute reservations (again, something they did on the previous AP reservation system).
Granted, this comes with the thought, "what would make that worth it for those buying a pass if they can't even go the first half a year they have a pass?" Again, my guess is it could just activate the day you first use it, the restriction of how many can buy an AP while opening that number up wider as months go on, and with limited amount of reservations, eventually everyone will get a turn if they're hard pressed to get one.
I personally wouldn't be too mad if it worked like, "every week, we are selling a limited amount of APs." 10,000 or however many a week. If it's 18K in the parks per day, with 30%/6K of those being able to be reserved, that's 12K regular ticket holders being let in which isn't too bad IMO. If the amount of AP numbers being bought is staggered, within a month everyone who first went will have had a decent shot to get a reservation and hopefully within 2-3 months, restrictions will have loosened up way more and obviously adding a higher percentage of people in the park.
Within 10 weeks of limited AP buyrates, you have 100,000 APs. And hopefully by that point, you'll now have a higher capacity limit. If capacity gets limited to a rise of cases, AP buyrates could slow down with the ability to pause your pass for a limited amount of months (think AMC A-List).
It can be done. Just a bit tricky. I don't know the exact logistics or legalities of them being able to do that, but it SOUNDS doable.