Undertaker is a legend and will be cheered always anyway...
They don't need a leader, at all. And Undertaker would just be really random. I hope they don't give them a leader, and I seriously hope they don't make Ryback the leader as that makes absolutely no sense. But hey.. it's the WWE right.
Taker can only lead one kind of group...one that fits his gimmick. He already did that with The Ministry. But Shield? Don't see the reason why he would. Plus he wouldn't take a beatdown and have two matches if he was the leader.
"What did we do that was wrong?
We didn't know it was wrong.
Fun is the one thing that money can't buy..."