The only reason I see why bitcoin will not work as the ultimate currency used by all is simple:
When all the bitcoins are minded there is no possible to way to get any more, nobody will want to spend anything because it will ultimately be the most valuable thing, and besides how the hell do you handle a deficit or surplus when everything is being done in the same currency and nobody can make more of it.
Ultimately we come back to the gold standard that had the same exact problems and blew up. The only thing i can envision for bitcoin in the future is to make online trading more efficient, but seriously there would have to be an unlimited number of bitcoins to solve the golden standard problem.

Your thoughts, let the flames begin!