My personal opinion is that all of the DVC resorts on the planet constitute only a drop in the bucket in the supply of room-nights in the immediate WDW vicinity...and therefore, DVC expansion would have ZERO effect on the parks.
My prediction is that DVC continues to expand for many years at WDW. They have plenty of room. Park attendance is driven by the economy -- not by onsite room availability -- and those folks have to stay somewhere. The Mouse might as well get as many of those dollars as they can.
As far as the effects on existing members, I'm quite sure Disney doesn't care about that at all. They already have current owners' money. Their only concern is future sales.
Besides, new members from expansion are just using the same system and following the same rules as everyone else. If I'm an owner at XYZ DVC resort and I choose not to make a reservation during my 11-month booking window, whose fault is it if an owner of SSR snatches the last availability in their 7-month window?
For resorts away from Disney themeparks, I think they make sense only in very limited scenarios.
I think a resort in Hawaii makes sense for several reasons -- primarily as a draw for a rapidly growing Asian customer base. I'm not sure I would have built it at Ko Olina, but Disney obviously knows more about that than I do.
But National Harbour? Naw. Why? Location, location, location. Who the heck wants to stay
there???
Ski resort? I certainly like ski resorts, but I don't see any Disney advantage there. If anything, they're at a disadvantage to companies like Hilton, Marriott, Wyndham, et al.
Cleveland? You know, I actually did not know that Cleveland was a timeshare hotspot! I feel so clueless.

I'm gonna go check RCI and see what they have there -- I haven't been to Cleveland in years!
Castaway Cay? Maybe. We could get some immigrant rafts, and if we could figure out how to drift them across the Gulf Stream without ending up in Scotland, we might have a shot at getting there. Other than that, I guess we'd have to helicopter folks in from Miami.