No mainline games, no Prime games, not even remakes or reboots of older games. A completely new Metroid spin-off. It could have the same gameplay with different characters and location or we could see Samus in a whole different game. Pinball demonstrates that the possibilities are endless.
So, which is your wildest Metroid dream?
Possibly a very boring or lame idea to some, but I think a lore-heavy game focusing on the Chozo could be fun. Maybe a JRPG or regular RPG would be cool.