As
Doom85
and
DeafTourette
have pointed out, the big flaw with this is that MLK was a real person who fought for civil rights. Making him a white alien would be crass and offensive.
What you could have said is imagine Marvel introduced the
Orishas who are the Gods of the West African Yourba religion. Then they decided in their own version that these beings were actually aliens. Then went one step further and made say,
Shango - who is the God of Fire, lightning, dance (as well as other aspects)- a middle age white man. Personally I think that would go down like a lead balloon and be called out even if it isn't a real historical person. Anyway it's a better example than MLK ( No offense to you, but why do people always try and say "lets race swap MLK"? So bizarre and really lacks creativity)
Anyway, slightly off-topic, but any media featuring the Orishas would be pretty epic.