I would like to play as him, but even if I don't, I would still like to play alongside him and talk to him. He's one of my favorite characters in Halo, even if he did kill millions of humans.

I don't know if we'll get to play as him. We'll probably see him fight but I don't think he'll be more than a supporting character now that he has a whole faction of elites to run and is a political figure with ceremonial armor :/

I'm thinking that is only his ceremonial armor. Looking at the helmet, you see it is very open in the front, not ideal for combat. But his helmet in the picture above, from Halo: Escalation, that's a combat helmet.It's sealed up in the front, and looks intimidating. I think he'll do politics and combat in Halo 5. He won't be reduced to just a narrator. He may not be playable but Thel 'Vadam won't be sitting around when there is work to be done.

I feel like you could be playing as Locke and chief only