If this happened, they wouldn't stay at the tower, but current owners are still staying at the resort though, and I think that's the main thing people care about. The question of where to stay has been mentioned here many times and most will discuss the pools, restaurants, walking distance, skyliners, monorails, and balcony for the reasons they love the resorts.
I really don't think making it the same association would impact the booking window, and if it did, I think it's much more likely it would impact current poly owners more than new owners.
Historically, the lowest point rooms are the first to go at 11 months for the most part and poly rooms tend to be wide open at this point. That could definitely change if it was the same association. One bedrooms and rooms with higher point views at all resorts tend to hang around longer and I doubt poly will have a different trend there.