While I understand the irony that it would be to cast Fast and Furious’ Vin Diesel as the silent king of the Inhumans after having him in another Marvel role that solely requires his voice, I don’t think he’s the appropriate pick for this role.
With the Inhuman’s story now mostly TV-bound, the actor chosen for this role needs to have a background in TV sequential storytelling. Who better to do it than an actor who already worked on an ABC show: Daniel Dae Kim (Angel, 24, Lost).
Kim’s extensive TV resume backs him as a viable choice for this role. If you know him better as Jin-Soo Kwon from Lost, like I do, then you can agree that his mostly-silent presence as Jin parallels that of Black Bolt. It also helps that the man’s presence screams regal.