Yea i don't think M'Baku is going to be a villain. I recall one podcast person predicting they may have a robinhood and lil john type dynamic in the sequel... now granted, the last thing of robinhood i remember is the animated movie about a fox, when i was like 5
so i can't speak on what that comparison even means. BUT i could definitely see T'Challa and M'Baku being that fun duo that ppl see in a T'Challa/Namor light. i.e. M'Baku has very similar traits when it comes to being a quip-ready ass.
Also, if you notice at the end after BP beat Killmonger and T'Challa enters the throne room as king again, M'Baku now has a seat there. So pretty much all 5 tribes are united now.
So i honestly don't see them doing a retread of that conflict. And i also agree that the whole "so and so" vying for the mantle is played out, imo. One movie about it is enough for me. I'd like them to adapt/modernize different storylines.
I disagree about Monica Lynne tho, I think Nakia is likely the best MCU love interest the studio has ever crafted. I don't think he needs another love interest, unless it's just chicks who like him... or they do a spin where it's a crazy bytch that's out to kill Nakia out of jealousy [a reversal of what Priest did]