The problem I have with having Yasuke as a main character is as follows:
Assassins Creed at its core has always been about exploring cultures through their most iconic time period, from the perspective of a person from that culture, with an exception of AC3, where the main character's mother was Native American and father was white, but done so to explore the history around colonialism.
I welcome the idea of an Assassins Creed game within central Africa with an African man/woman as its lead, but I think we can all intuitively understand how wrong it would be to give one of the leading roles to a white character.