I don't think there is a clear successor or even decent alternative to Naslund, so let's hope he doesn't mind keeping it for at least one more season. Maybe next year, if it's too much of a burden on him and he steps aside, Mitchell or Morrison will have made a case, I think they both have potential. Regarding Morrison, the captaincy affects players differently, some of them find it a distraction (I think Lacavalier made that point once) while others find it a standard that forces them to raise their game, Morrison might find this to be the case, Mitchell I think just needs to spend some time here but he's the natural leader type.
Also agree that we need leaders other than the captain, and that is another reason to keep Linden around for one more season, plus I think he'll be rejuvenated without the NHLPA to deal with during the offseason.
I'm going on what other people (I think Media Man) have said on this site, but while Cooke is an aggressive and hard working player on the ice, I've heard that he's a bit of a punk off-ice, and might not have the respect of the team. Moreover, it's not the best example to pick fights with people, turtle and then count on your teammates to bail you out, especially if he's wearing the "C".
Ohlund is a solid player and a leader by example, but I don't see him as enough of a take-charge passionate voice to be a captain.
I also hope that whoever we pick up for RW has size, grit and leadership, we're lacking the first two on the top six and the third overall.