I think naming captains is pointless, personally.
If he's a leader, he'll lead. Shouldn't need a silly badge or title to do it.
Sometimes it's helpful having a single defined leader. But it's important for that leader to demand the necessary respect.
If you don't have a single leader you run the risk of factional leaders and an increased chance of a locker room split.
The trouble comes with who that person is. Al seems the obvious choice but even he could be gone in the summer in an AD trade.
It's either Al or Marcus Smart for me. There are other leaders, just like there were when Pierce was captain. However those two have the longevity and the credibility to make it work