A Switch-exclusive Mario Kart could do the trick. However, I don't see any reason why Nintendo would actually make one considering how well MK8D is selling despite technically being a port.
Other than that, another mainline Pokemon title could do it later down the road (2021-2022).
Also, a new classical 2D Mario title should be able to do so. And unlike with MK8D, I don't think Nintendo is satisfied with NSMBUD and/or SMM2 sales to let that opportunity pass.
Now this may be more out of left field, but how about a successor to Tomodachi Life, maybe?
Finally, maybe Ring Fit Adventure could reach it in the end. It doesn't look like it's sales were to slow down anytime soon, and shipments still sell out more or less as fast as they come in.
The Nintendo eShop rating Thread: http://gamrconnect.vgchartz.com/thread.php?id=237454 List as Google Doc: https://docs.google.com/spreadsheets/d/1aW2hXQT1TheElVS7z-F3pP-7nbqdrDqWNTxl6JoJWBY/edit?usp=sharing
The Steam/GOG key gifting thread: https://gamrconnect.vgchartz.com/thread/242024/the-steamgog-key-gifting-thread/1/
Free Pc Games thread: https://gamrconnect.vgchartz.com/thread/248138/free-pc-games/1/
