The title of Captain is given by a coach to a player- hopefully a player who is also a leader.
On a team, a leader, by definition, is somebody who others on the team will listen to, follow/emulate, and come to for counsel.
You can have an official, designated Captain/leader, while also having other players who are leaders in their own ways. You would expect Amare or Felton to emerge as leaders this year, but there is no doubt in my mind that Turiaf will be a kind of spiritual/emotional leader on this team.
No actual need to name an official "Captain" at this point, IMO- MDA should let things evolve at their own speed.
None of our holdover players have the experience to be leaders at this point. I've said before that I believe Gallinari will eventually be a leader, and I think that Douglas, if he produces, has some leadership ability, but both a few years to go before they can be considered team leaders.
No man is happy without a delusion of some kind. Delusions are as necessary to our happiness as realities- C.N. Bovee