Future captain means after Del Piero retires, because personally I don't think he is going anywhere.
If you ask me how should the arm band go in Juve at the moment I'd say like this:
Del Piero
Ferrara
Tacchinardi
Pessotto
Birindelli
Zambrotta
Thuram
Buffon
Nedved
Camoranesi
Cannavaro...