After blasting off from SR388 with Samus and Baby Metroid and defeating Metroid: Samus Returns, the credits will roll and then a Post-Credits Epilogue will be shown. Here, a yellow Hornoad will suddenly appear and begin to tug at a claw, presumably one that belongs to Ridley. However, before too long, the Hornoad will be attacked by a blob-like creature, one that actually resembles an X-Parasite from previous games in the Metroid Series. After being infected by this blob, the Hornoad will suddenly turn purple and become very, very angry (almost possessed).
So what does this little cutscene mean? Well, it could be a teaser for a follow up game to this one. Most believe this could lead to a remake of Super Metroid - the original sequel to Samus Returns - which could then lead to the remake of Metroid Fusion, the final game apart of the Metroid Timeline. If you may recall, Metroid Fusion actually begins with Samus shooting a Hornoad much like the one seen at the end of the epilogue, and after doing so, she herself becomes infected by the X-Parasite.
Only time will tell what this Epilogue truly means towards this remake of the Metroid Series, but it's looking more and more favorable by the passing day that the story of Samus will indeed continue!