Rumors are pleantiful--hard facts are difficult to come by.
The most popular rumors involved the Contemporary. But we've also seen the Poly and AKL mentioned as possible
DVC sites.
But with each rumor comes more reasons why those same areas may not be feasible. Some people claim that the ground is too unstable for further construction at the Poly. Others claim that Disney is afraid to put money into the Contemporary because they don't know what they will do with the resort over the next 50 years.
So take anything you hear with a grain of salt.
I've always thought that adding onto an existing property made a lot of sense from the Disney's POV. They don't have to construct things like the check-in building or recreation areas (pool, boat dock, etc.) Yet when the DVC component of the resort opens, they begin to split the operational costs of these areas of the resort. But again that's just my opinion. I'm sure there are drawbacks as well.
As I understand it, the Eagle Pines resort was actually announced before Saratoga Springs. However at some point in the development it was determined that the old Disney Institute was too run-down to continue operations. Rather than sinking millions into a Disney-funded rehab, or leave the resort sitting unused (right across the lake from Downtown Disney), they moved SSR ahead of EP on the slate. The rest is history.
It stands to reason that Eagle Pines would be the next dedicated DVC property given all of the development work that has already occurred. There may have even been some land prep work performed in anticipation of construction, but the site has been sitting dormant for some time now.
All signs indicate that there is still a strong market for DVC ownership at WDW. Certainly they will eventually reach some point of saturation, but only sales figures will determine that.
Off-site resorts are currently not on the radar.
Final note: Eisner did appoint a new head to the DVC program back in the fall. With new management comes new ideas. It has yet to be determined when/if this appointment might change the overall direction of the program.