Until it's proven differently, and it very well may be; I think the current booking window move to July 1 is much more about controlling capacity than having anything to do with an "opening date." If their goal is to keep the main gates at, say 50% or less, then they know what capacity it takes in the resorts to balance locals and those staying outside the parks to balance that out. When the resorts hit that number, it makes sense to close bookings for that period based on what they know will be open in whatever manner.
I wouldn't read too much between the lines on the "July thing" if it was me. It all makes perfect since if you step back and look at it.
FWIW, they can't effectively limit DVC resorts, and I'm equally sure that's all balanced into the equation as well. If there's one thing Disney excels at, it's data and data mining. They don't think. They know. Everything, when it comes to the numbers.