It's either that or he just wants a good burger to chow down on. The part about him being the conduit they used does suggest something along those lines. I just wonder what he could be feeding on.
Also, why do I have a feeling Stephen might be under the ground in his tomb also?? I expect at the very least he may be able to talk to T'Challa with what looks like his old Eye of Agamatto amulet. Doom had given him a different eye to use.