I don't think either Super or Fusion need a remake. They are both fine as they are. Re-releases, that's a different story. It'd be nice to have Super and Fusion (and Zero Mission) on my Switch. But otherwise no they don't need to be remade. They look and play fine. Metroid and Return of Samus were in much more need of being remade. Plus I'd rather them spend time making new Metroid games than revisiting older ones.
This is usually the exact response I see whenever I give my thoughts on the topic now, but I guess Fusion I'm just a bit more passionate for seeing reimagined, being one of my most replayed titles in the series aside from OG Prime. Super Metroid will at least remain timeless with the mechanics and things it has that are still unique to it, but Fusion easily feels the most dated now, despite being perfectly playable.
It is interesting that a Fusion remake was apparently MercurySteam's original idea pitch for a Metroid sidescroller before they were brought in to officially remake Metroid II; I'd be lying if I said it didn't make me curious as to how their take on Fusion would be. I think Fusion particularly would benefit pretty well from MSR's new mechanics (the aeion abilities which they could even have new ones for, etc), and would like to see how they'd give the combat and areas & bosses more depth than the original. Plus being the closest Metroid to a survival horror, I'd love to see things like the SA-X chase scenes remade with better AI, and after what Mercury gave us with Proteus Ridley, I
know they'd make Ridley-X a far more memorable encounter than what he was originally... Even the SA-X fight could've been much better designed.
Perhaps most of all though, a Fusion remake could tie in/lead up to the Fusion sequel we've all been waiting for, whether through some Chozo Memories esque way of storytelling or other means.
I guess as it is though, would save another remake for bringing the series back out of another hiatus or something (that's what Samus Returns did which in part made it special), while focusing on just new games until then, tho would take Super/Fusion remake over a Federation Force 2 at any time.
And regardless of what we get next aside from Prime 4, something something Ridley amiibo functionality.