Wow, good showing for Metroid only being behind Pokémon and Mario Maker!
And wow at it beating Fire Emblem even though it came out after, so many people were telling me how Fire Emblem eclipsed Metroid as a Nintendo series ;)
Metroid's showing is great because
-It was a remake without much hype behind it
-It was made by an untested third party studio
-It was on the 3DS rather than the Switch, and many big-spending early adopters had left that console behind
-The fans had been in open revolt for years
-3DS is easy to pirate on (I know multiple people who pirated Samus Returns)
-While very good, it wasn't one of the best Metroids
So all told, it's really encouraging. If they could get Metroid Prime 4 out while the Switch is still hot and make it a great game I think it would do amazingly.