The new CNAS policy brief is up at

http://www.cnas.org/node/3578

my comment on it was: I think the paper is generally on target. And I too think that a stable Afghanistan is NOT impossible, but would take hard work, which the US may not be willing to do (or capable of doing? one has to consider that imperial decay may already be past the point of no return).
Some commentators feel that this overstates the importance of the "af-pak haven" for AQ. While it is true that AQ does not really NEED a haven to continue as a terrorist group, a victory in Afghanistan would make a huge difference to their prospects. The difference is the difference between Baader-Meinhoff and a serious worldwide threat. Defeat in Afghanistan would make the whole AQ project seem even more of a fantasy and a cultish fringe act. They would still get the occasional Saudi willing to walk around with explosives up his butt, but such nutcases would not have wide support in the Muslim community (which would see them as dangerous crazies, not a serious alternative to the current crop of corrupt "leaders"). On the other hand, if the US goes down to defeat in Af-pak, it would translate into a huge boost to the jihadi project. They would have proven their point: they got a superpower to walk into their trap and they defeated the superpower. Palestinians and others Muslim communities with grievances (real AND imagined) do not have to regard these people as medieval crazy morons who are more dangerous to their own community than they are a threat to US-Israel. Instead, they can see them as a real alternative to all the "corrupt puppets" the US has supported all over the Muslim world. Increasing numbers of Muslims will start thinking afresh about joining the cause or at least hedging their bets. Maybe no dominoes will actually fall, but many dominoes will have to be rescued using brute force, nasty tactics and extreme violence. Baader Meinhoff never got that far.....