I'm Alliance all the way for gnomes, so most of the horde stuff didn't seem that great to me. Thrall was always that iconic hero that I just didn't care for since everyone treated him as if he lacked faults, except when he needed faults to be cooler, or something. I didn't dislike the Tauren, but it's a bit tiresome that they're always presented as these peaceful types, when the first thing my little proto-tauren do is go out and kill local threats. That's not "wrong", but people paint them as somehow "holier than thou" when it comes to violence...

Anyway, the point is, I like VolJin. He seems to be a capable, well rounded leader. He is smart, but has a temper, he is also smart enough to realize he lost his temper! :) He's not afraid of a fight, but doesn't seem to go out of his way to look for them.

Also a possibility that the Loa have warned him of the Zandalar as a threat!

IMO, he turned down the Zandalar offer because the Dark Spears will not submit to ANYONE. Voljin didn't do much under Thrall, because Thrall understood that. It makes sense to me that Voljin kept a low profile during Thrall's reign. Under Garrosh, he made it perfectly clear that the trolls were not subordinate to the orcs, they were in the Horde because they wanted to be and because they believed in the alliance.

To join up with the Zandalari and the other tribes, the Dark Spear would become lessened again, even if the trolls won. (Especially if the trolls won, I guess.)

I look forward to the day he gacks a leader for the horde. Maybe Sylvanas' time has come, or maybe Garrosh needs an arrow as promised, but I'd like Voljin to be there to do it. :)
(Though I can't see him being Warchief)