Please note that this is a rumor based on tweets from Emily Rogers. While she's not batting a thousand, her recent rumors regarding the Nintendo Switch have been pretty accurate. Take everything hereafter with a grain of salt.
According to Emily Rogers, Super Mario Switch is closer to completion than many realize. So much so, that she believes it could be a launch title for Nintendo's new system:
I wouldn't be surprised if 3D Mario ends up being a day one launch title for Switch instead of Zelda…That's all I'll say on that.
— Emily Rogers (@ArcadeGirl64) November 5, 2016
That's not to say that Zelda won't/can't be a launch window title. But 3D Mario was much further along in development than anyone thinks.
— Emily Rogers (@ArcadeGirl64) November 5, 2016
This isn't speculation. I'm basing this off things I've been hearing for 3-4 months now. 3D Mario sounds like it's practically finished.
— Emily Rogers (@ArcadeGirl64) November 5, 2016
That doesn't sound too farfetched. Mario games are almost always in development, and the internal development teams behind Mario Galaxy and Super Mario 3D World haven't had a major new release in about four years. There's no way all they did was sit on their hands while they oversaw Zelda remakes, and Captain Toad: Treasure Tracker wasn't exactly a massive with a lot of development resources thrown at it.
She also says Super Mario Switch has more exploration than Super Mario Galaxy and Super Mario 3D World, which could position it as more of a Super Mario 64 type of game.
I don't know if there's a hub world, but this new 3D Mario on Switch has more exploration than 3D World and Galaxy. https://t.co/2Wq1kkWmpr
— Emily Rogers (@ArcadeGirl64) November 5, 2016
I certainly hope so. Exploring Peach's castle was a memorable experience, and that sense of adventure is something I'm sure many would welcome back to Mario games.