A DDO 2 project would need to have the backing of Warner Brothers. Warner Brothers owns more than one game development firm. I truly believe at some point in the future a deal will be struck to work on a new D&D mmo project. It can very well stay "in house" for WB. Noone knows where it's going. That was the reason for including the thought in my OP.
Whether there is a DDO 2 in the future, or just another D&D based mmo (much more likely), that's just a sidebar to my main topic which was how long do we see DDO in its current form, developing new content, and staying "plugged in" (these very well can have vastly different end dates). It's not in black & white, since we are talking about a license that is treasured in the gaming world.