I think Michael B Jordan would work great as Killmonger, though maybe they'll stick with his original name, N'Jadaka. I assume Andy Serkis will be back as Klaw, and Killmonger has the ready-made connection with him, with Klaw in the comics having killed N'Jadaka's parents when he was a young child and taken him around the world with him acting as his servant. They could play on that twisted surrogate father-son relationship, maybe N'Jadaka infiltrates Wakandan supposedly for Klaw's purposes but is later revealed to be acting for his own ends. Maybe they could even have an INFINITY WAR tie-in by having Killmonger get a hold of the Soul Gem - here a Wakandan artefact - which he uses to create his zombie-like Death Regiment army that he had in the comics.