Nintendo could potentially be making use of some new games onto the Nintendo Switch or 3DS. A ResetEra forum member noted that Wrecking Crew, Mario Super Sluggers, Rhythm Heaven, and Golden Sun were all trademarked by Nintendo, with applications filed on August 24th, 2018.
This doesn't mean that Nintendo is planning anything with these trademark filings; Nintendo renews trademarks often, but it's still possible that there's something new incoming for every franchise. At the very least, there's potential of these games being ported or remade. People have speculated that this may have something to do with Smash.
Author's Note: Do you want more Golden Sun and Rhythm Heaven? How about Wrecking Crew and Mario Super Sluggers? Any hope for them in Smash? Let us know in the comments below!