Imo, Fusion left a damn good set-up for Metroid 5.
SPOILERS:
She defied direct orders from the Galactic Federation and exploded the space station and a whole planet (again). I'd think that she's now one of the most wanted criminals of the galaxy. And this Metroid DNA on her own genetic code is also really interesting. Since the Federation wanted to use the metroids for other purposes, there goes another reason for them to want to track Samus, who still have to worry about the Space Pirates.
Oh please, let the next Metroid be an actual sequel instead of another interquel.








