doesn't T'Challa still technically have the King of the Dead powers? Not sure what is added for temporarily making him a vampire.
I would have pitched a team up mini series with Blade, with a race against the clock to prevent a fluke infection from taking hold of T'Challa during all the madness of the vampire hordes. If they want to go into the mythology of african monsters, that's fine.
I just hope that there is an obvious off-ramp for T'Challa's descent into vampirism that does not involve alternate world duplicates or clones (Krakoa?)