The advantage of adding PVB2 to the same association would be that otherwise the resale price for PVB1 would plummet, creating problems with ROFR and sales. Would you buy a resort with only studios when there is a newer Tower next door with a balanced number of units in different sizes?
While that could boots PVB2 sales, if PVB1 price plummets, then it will be competition for PVB2. Maybe you'd prefer PVB2, but what if PVB1 is half price resale?
I am not sure myself if this would really happen. It's difficult to make predictions with DVC and I'm usually wrong

I think 60% will be a new association. But people asked for things that would advantage Disney for the unique association, and this could be one.