Ya know, I almost wonder if Nintendo is setting themselves up to have another go at a new (completely optional) era of 2 screen at-home gaming. I think most of us would agree that the next Nintendo system is likely going to be essentially a Switch 2, and the original Switch and its variants are now at about 100 million units sold. That's 100 million people with a handheld gaming device.
The Switch 2 alone will likely be it's own single screen hybrid system like the original Switch, just more powerful. But Nintendo will know that a huge portion of the people that will be buying a Switch 2 will already have an original Switch, sure some will probably sell their original to buy the Switch 2, but even still with over 100 million of them out there, it's a safe bet that they'd still have many millions holding on to their original model as well as buying the next gen version.
So, why not have the Switch 2 able to optionally connect to the original Switch, where the OG Switch acts in the same was as the Wii U GamePad did for the Wii U, you hold it portably and control the Switch 2 with it, while also being able to use the touch screen of the Switch 1 with what is happening on the Switch 2. Hell, this can already happen with 2 Switchs as it is, with Namco Museum and the Pac-Man Vs. Companion app, where one screen plays as Pac-Man and the other plays as the ghosts. They could reimplement Wii U features for Wii U ports or dropped features that were planned like the on-the-go inventory in BOTW and the always on map for more quickly fast traveling, etc. etc.
It would have to rely on companion apps on the Switch 1 and whatnot, which probably could get a bit larger in size depending on the game they would be connecting with and how many assets of it the Switch 1 would need access to, but this is still totally feasible. And it's kinda a clever way to get everyone (that would want it) the GamePad controller without feeling like they had to pay extra for a controller with a screen built into it.
Frankly this all just makes too much sense to me not to do, it couldn't hurt to try, especially since some implementation of this kind of stuff would probably take very little additional programming per game, as really all it is, is wireless LAN multiplayer. So if Nintendo doesn't even give this a try when the iron is hot with the launch of their next device, I would say that's a sign that Nintendo is just done entirely with the idea of dual screen gaming. I hope that isn't the case.