DVD's primary function is to create and sell new pools of points to us, the loyal customers of Disney, and to do so in a manner that maximizes profits and meets both tactical (short-term) and strategic (long-term) business goals. Spending a gazillion dollars building a shiny new tower and then adding it to an existing resort that is about a million years old (and shows it) does not really further the stated strategic goal of enticing direct sales by adding restrictions to resale points. There is no evidence to suggest that DVC is backing away from that business model.
It makes no sense at all to add the Poly Tower to the existing association.
But hey, I could be totally wrong