Why not? It's not actually any less plausible than any other variation. No conceivable scientific process could produce a human being who is nearly identical in personality, appearance, birth date, and major life events to a human in another universe and yet has a different history and cultural background. Neither cause-and-effect nor sperm work that way. Clearly, then, multiverses are governed by some form of meta-level, narrative-based imperative - certain arbitrary players and events are fixed (there is a Reed Richards, smartest man alive; he will be bombarded by cosmic rays), while everything else is mutable (he might come from a modern Western society or a post-apocalyptic Stone Age, he might be raised to science or to magic, he might be a friend of man or a supervillain, etc). No reason that race or gender should end up in the static column when equally relevant stuff like who won WWII is freely fluid.