Hi Dean,
From a DVC systems perspective, I, too, do not see much downside to expanding at WDW. However, if DVC continues to add a new resort to the WDW collection every 3 or so years, from now until 2042, then it seems reasonable to assume that the Parks & Resorts division would have to account for this expansion through increased entertainment, dining, and transportation.
It is not uncommon for the theme and water parks to close after reaching capacity (phase 3). It is my speculation that future DVC growth may be predicated on overall guest area enhancements and expansions.