That does seem to be her thing.
What do you think her chances are of being brought back for MP4?
Zero. Her very being is inextricably tied to Phazon, which at the end of MP3 was completely wiped from the galaxy. Unless they retcon that, and it turns out there is Phazon out there, then she's gone. And I believe Kensuke Tanabe has said that the Phazon story arc is definitely over with, so by extension, Dark Samus, too.
People like to say "But she's the namesake of the series, so she
has to come back!" But, for one, I'm pretty certain Metroid Prime died, and Dark Samus is a new entity that is an incarnation of Metroid Prime, but not the same being. And two, Prime is simply a brand for a style of Metroid, no longer associated with the final boss of the first game. Hence, Prime: Hunters and Prime: Federation Force.
As much as I'd love to see more of her, I think she had a fitting run. Two games with prominent roles is better than many other Metroid characters. And now that she's playable in Ultimate, that's all I'll ever need from here on out.
Dark Sammy was my 2nd choice after Ridders
She and Chibi-Robo were my top-two. I voted for her in the ballot because Metroid needed another rep, and Ridley was clearly denied, so I took the opportunity to vote for her and hope she'd pass since she isn't too big and her AT showed her potential. I thought, after Ridley, she'd never happen, but I was happy with Ridley. But... here we are.