>>715920707
It speaks to how the games are designed that Metroid has never had any "alternative" playable characters. I think that every single Castlevania in that style has had at least one outside of Circle (which just had alternative playstyles instead). I'm just not sure that Metroid is built for the kind of thing, even CV often has to cheat in a couple moves for the alt characters so that they can actually explore properly. Metroid is too intentionally designed for each ability with its passages and secrets, I think it'd need to be completely overhauled for another character.
The only game that could've gotten away with it is Fusion funny enough, if they let you play as a rogue SA-X or something and cut out the info rooms.