I like that idea.
And to be honest, I would actually enjoy some "alone" time, where the PC has to overcome some obstacles on his own.
I would like to explore the master/student relationship a bit more, and I think I would like a good chunk of the PC side of the game to be just him and his master, and perhaps later just him and his student.
But I agree, seeing things from a varying perspective can be a lot of fun. I love the little ways that Splinter Cell 3's coop ties into the main plot of the single player gamer. And I think it would have been neat to have been able to go with Canderous when escaping the Leviathan.