All I am seeing right now is everyone fighting over capacities and legal terms.
Quite frankly, no one knows exact numbers except for the parks themselves. They do not and to my knowledge never have and likely never will release exact attendance for parks. Attendance is considered a trade secret. The only numbers you ever see are either estimates or a nice rounded off number for marketing purposes. The closest estimates you are going to get on attendance will come from the annual TEA/AECOM Global Attractions Attendance report.
Capacity is different from attendance. While yes restaurants, theaters, and individual buildings have governmental imposed capacity limits parks themselves don't have such set numbers. This is for the reasons
@Zachary gave. Parks give their best guess for capacity in the moment based on various factors. I know for a fact (from personal experience) that BGW doesn't count individual people as capacity. They measure their capacity by parking lots. If the parking lots are full and there is absolutely no space to park any vehicles, then they consider that closing the park due to capacity. WCUSA is even worse because they will park cars taking up any space in the grass, gravel, even in the middle of the road to prevent turning guests away.
All you can do right now is to gather data from TEA/AECOM's report and based on that create an estimate for what an average daily attendance might be. For example, according to their 2018 report, Magic Kingdom had approximately 20,859,000 guests for the year. When divided into 365 days, that gives an average of 57,148 guests per day (Side Note: I did round to the nearest whole number). So I would feel confident in saying when taking into the current situations requirements, if they were going to cut capacity, I would imagine their goal would be to restrict attendance to a daily 14, 287 guests per day to start with. For comparison, BGT had an estimated attendance of 4,139,000. By dividing that into 365 days, they had an average of 11,626 guests. Meaning, if they were to restrict their capacity to only a quarter of that, you are looking at only 2,907 guests per day.
Basically, Magic Kingdom would permit a slightly higher than average attendance than BGT.
Disclaimer: The figures I have provided were provided from TEA/AECOM's 2018 attendance report which is only a estimate and not exact. It is used in the industry as a guiding point, but not as an accurate science. And to add on to that, my calculations are just estimates based on averages and I'm not truly sure what we can expect to see park capacities reduced to.
The other issue is pass usage and reservations. Quite honestly, this drives me crazy that people think this is new or surprising terms when it comes to not guaranteeing admission for passes. This is the basics. Just because you purchased an annual pass does not mean you can use it every day without fear of being turned away due to a multitude of reasons. The biggest reason being park capacity. If they were to give every pass holder guaranteed admission regardless of capacity, that would truly be a nightmare.
While I am not trying to convince anyone that this is definitively how it will work; I believe there is no ratio between passes and single day admission. They most likely will have a system that will take X amount of reservations per day. I can see this being a similar setup compared to how FastPasses at WDW are reserved. Availability opens up and people purchase their ticket/reservation, and as spots are taken the options begin o disappear. Spots may open up last minute if people choose to cancel their reservation.
I don't understand why there has to be restrictions? It is a very simple and straight forward process, as I would imagine it being. People should just be cognizant of the current situation and realize, there will be less people permitted and should therefore make better plans or arrangements. They can do that by simply taking the time to ensure they are able to get everyone reserved far enough ahead of time.