At this point, I think it all comes down to what Knott's chooses to do.
If Knott's chooses to deal with the logistics of allowing put of state visitors before June 15th, Disney will likely follow suit, because they actually have a very low demand level right now and unless they decide to bring back annual passes or something like it, that isn't likely to change without out of state visitors. But at the same time there wouldn't likely be enough out of state visitors to make the headaches worthwhile if Disney were the only park in Orange County allowing them.
Knott's may have more of an incentive to allow out of state visitors, as they have season passholders from other states and there is a bit of a logistical issue with how to handle that, especially any that have the highest pass level. Right now, the new expiration dates end before any of the seasonal parks would open for the 2022 season and since add-ons are also extended, this means extending to early May has no real impact on the other parks. But if out of state visitors aren't allowed, it isn't really fair to them to only extend to early May. So, I can definitely see the potential for Knott's to.open up.to.out of state visitors. The all season dining.in particular is problematic due to Costs associated with it.
SeaWorld had this problem on an even bigger level, as they have a lot of Platinum passholders out there in other states that hold SeaWorld San Diego as thier home park because they were grandfathered into the same low price for life on monthly payments. This is likely why they were so quick to jump.on board with allowing out of state visitors, as it solved a major issue for them. SeaWorld introduced all season dining for 2020 and so they are in a bit of a bind with that.
If Knott's sticks to in state only, Disney will likely do the same.
I would predict Universal will do whatever Disney and Magic Mountain do.
Magic Mountain is of course the other wild card here and may impact what Universal does, in which case Disney would have little choice but to follow and they are likely.in a similar boat with thier meal plans.
Now the parks with all season dining may do the math and figure out 6 extra weeks of all season dining for out of state visitors in the form of an extension won't break the bank, but there is no guarantee that the state will open up on June 15th and things may be tight for them already.
So ultimately, it is anyone's guess as to how this will go, but ultimately it will likely be Knott's, Magic Mountain and SeaWorld driving the policies in this case.