Dude, loved the post.
Although I don't know much about Dark Samus, her stage could be the place where we fight her in Metroid Prime III: Corruption, something like this!
This is the Sanctum in Phaze, a planet made out of Phazon so it's like Dark Samus sort of homeland!
And as for another metroid stage, I would personally like a Tallon overworld one from Metroid Prime: 1
The Sanctum does sound like a cool stage idea, and might even be better than my own. Like I said in the article, I'm not too familiar with the Prime series, having never played the games myself, which led me to pick a basic location from the Prime trilogy.
The only Prime game I haven't played is Prime II: Echoes. I have the trilogy waiting for me but I haven't had the time to really get into it. But I am familiar with the other prime games since I've played them several times, that's why I wanted to point that out o/: