I really think Aulani was all due to Joe Rohde's passion for the project. He's from Hawaii, and it's clear from his previous projects (Animal Kingdom, Adventurer's Club, Trader Sam's, etc.) that he loves the tiki lifestyle and all that goes with it.
That being said, Hawaii is an ideal location for a non-park DVC resort. They found a great location in Ko Olina, and probably got a deal on the land because the economy has been poor for so long. For the longest time I secretly thought Disney would end buying the Grand Wailea resort on Maui and turn it into a combination hotel/DVC, calling it "Disney's Grand Hawaiian Resort & Spa" or "Disney's Grand Wailean Resort & Spa". When the original owners went belly-up and the place was sold for a song, I was really surprised it was Hilton who bought it and not Disney. But I also understand the reasoning--they probably would have spent as much getting the Grand Wailea up to Disney standards as they did to build Aulani from scratch (money Hilton hasn't invested in the place, by the way). And Oahu is much easier for Asian tourists to get to than Maui, who make up a sizable portion of Aulani's clientele.
I suspect there will be additional non-park DVC resorts in the future. Personally, I'd love to see one in Las Vegas. The defunct Ritz-Carlton would be the right location--away from the strip so the family "vibe" can be maintained, but close enough for visitors to go see the glitz of Vegas when they want to. DC is another busy tourist destination; I'm still incensed that Disney's America never got built, though. Maybe San Antonio (with excursions to the Alamo, Schlitterbahn, etc.) or Houston (Space Center Houston, which was designed by Imagineering)? I'm having trouble coming up with other domestic locations that have enough of a draw to make the investment worthwhile, but then again I never in a million years would have chosen Vero Beach or Hilton Head Island. When you consider how obscure those destinations are, they could really go almost anywhere!