Maybe Metroid could have its own version of Hyrule Warriors someday, and be called Galactic Warriors or something... Somethin like that has sorta been a fanboy dream of mine before Hyrule Warriors was even a thing, actually. To see Ridley fight/kill other hunters besides Samus.
Only problem is that Metroid has a distinct lack of characters to use, and Musou games are known for having pretty big rosters of characters, at least the recent iterations/spin-offs. So the roster would be like, six versions of Samus, Anthony Higgs, Ridley (both versions), Kraid and Super Metroid Mother Brain (Final Boss Form).
... Honestly, I'm joking around, but the more I think about it, the more I kinda want to see it.
EDIT:
Just thought I'd entertain the idea of Metroid Musou. We'd probably see:
* NES Metroid Samus
* Super Metroid Samus (Varia)
* Super Metroid Samus (Gravity)
* Other M Samus
* Prime Samus (Normal)
* Prime Samus (Phazon)
* Fusion Samus (Varia)
* SA-X
* Dark Samus
* Anthony Higgs
* Adam Malkovich
* Ridley
* Roidley
* Meta Ridley
* Omega Ridley
* Mecha Ridley (Incomplete)
* Mecha Ridley (Complete)
* Kraid
* Mini-Kraid
* Draygon
* Nightmare
* Super Metroid Mother Brain (Final Boss)
* Phantoon
* Kanden
* Weavel
* Spire
* Sylux
* Noxus
* Trace
* Gandrayda
* Ghor
* Queen Metroid
* Omega Metroid
* "The Baby"
* Crocomire
* Torizo / Gold Torizo
I'm sure there's way more there, but shoot.. I guess I was wrong about Metroid Musou having a lack of playable characters. I am behind the idea 100%.