That's what I was thinking too, part of Van Buren was going to be set in Nevada so Obsidian may very well be developing Van Buren (on a smaller scale) in the Game Bryo engine for this "spin off". I'm looking forward to learning more regardless.
Rather doubtful, since a recreation of Van Buren's plot would require a much bigger game than what New Vegas is likely going to be. Although maybe if New Vegas does well, they might get contracted with a bigger project that could do Van Buren justice?
I do hope, however, that the game will have lots of references to the events, locations and characters from Van Buren, so that they'll at the very least be made officially canon.

Maybe e.g. Caesar's Legion could appear? Daughters of Hecate? References to the NCR-BOS war? Characters from the nearby and NCR-run Hoover Dam?
As for Obsidian, some of their members might have been involved in making good or great games once upon a time, as much as some might argue Beth made great games when some around these boards claim Daggerfall or Morrowind were the pinnacle of everything good.
Bethesda has fewer Daggerfall developers than Obsidian has FO1 and 2 devs.
Okay this game will be released on PC, XBox360 and the PS3. As such which one of Obsidian's engines do you think will work on all of these systems by 2010? Not Van Buren. I'm sure it's pretty safe to assume it will be Gamebryo, Fallout 3's engine.
Yes, it's pretty certain that to make it in a year, they'll have to use FO3 engine and many of FO3's assets. Just like FO2 used lots of FO1's and was also made in a year or so.