As long as a villain is written like a threat aka not downgrading him... "sharing" a villain isn't a problem at all. Especially not in a maybe/maybe not wormhole time travel alternate reality situation.
It is only when villains are shared and they are treated like shit (Klaw the easiest example) is when it turns into a problem.
Kang being beaten by the combined might of a future maybe/maybe not wormhole time travel alterante reality galactic Wakanda is not a slight in any shape way or form.
Not only does The ultimate conqueror vs. a king of an undefeated nation almost write itself... but Kang is written a lot of times to playing the long game, moving stuff around like chest pieces, to get the outcome/future he needs... hmmm... who does that sound like?
Kang vs Priest T'challa would be epic.
So, let's stop talkign about it until we get a new writer so it isn't ruined like the Galactic Empire thing has been ruined. Redjack, put it in your backpocket!