If they do put in Monstropolis, which I wouldn't put past them, there is no way they try to tie it into Hollywoodland. They'll make it its own land. They're too smart to try and feed us the "it fits in Hollywoodland because its a movie" argument. Also, what better way to advertise the parks than a whole, brand new land!
I think a Monstropolis theme is more comparable to Bug's land than Carsland. Could it exist in California? Sure, but it doesn't really do anything to represent the state. On the other hand, if you took all the 'Cars' references out of Carsland, it is still a well-themed area that presents an idealized version of a Route 66 desert adventure.