Been following the back and forth on this, this is my entirely headcanon likely false conspiracy to make sense of this whole thing.
Monsters was set to replace Muppetvision and that area of the park. They had concept art ready for D23 to confirm it. They was greenlit as late as July 17th this year, that's why you started to see a random article about making it a "historical site" (though it can't be with its age), that journalist got the tip they might be removing this. Internally some are fighting for it to stay and there's a campaign from them.
They knew removing would get heavy backlash, it is now with no confirmation. Muppet fans are very passionate and this is a realic of Jim's final works. Where I get into full conspiracy is I believe the rumors they want to replace HOP with Muppets, as that's a massive lightning rod headache for them and Muppets is something they still want around. That would soften the blow if announced the same time at D23. What threw a wrench is the unprecedented election withdraw late July. To not get too into politics if they closed HOP right before we get the first female president it would be a very bad look and they figured that out in a few days. So they have to keep HOP at least until after election, but that would also mean announcing Muppetvision leaving without a replacement which would be insane meltdown levels. So Monsters is just announced without a specific location as they aren't sure yet on final plans where to put Monsters or if HOP is shutting down soon or in 4 years.
There seems to be a last minute push internally to move Monsters to AC and spare Muppets. There's definite connections they are making with journalists and influences to push a final online campaign to save it, and also why you hear so many conflicting stories on what's being replaced. How that ends up is anyone's guess, many ways it could between multiple ride's fates
