While I do feel that we're going to see new hardware in 2021 and a platform evolution generation, rather than a scrapping of the Switch to start over from scratch on something else. Nintendo COULD hold off for years to come - as I'll explain in the next two paragraphs - and I'll explain how Gen 1 and Gen 2 can co-exist in the third paragraph.
The industry has evolved a great deal since the 1990s. The Wii and DS created an entirely new sub-market for the video game industry - and mobile + Steam have really run away with it making that pool MUCH larger than it was even in the Wii/DS era. That is, the AAA industry, and big studio game development in general has lost its dominance. These so-called "shovelware" games are what most people want to play... and to be frank, many of them are much more fun and satisfying to play than big AAA titles that are clones of things done dozens, if not hundreds of times before. All the triple A industry does is takes old ideas and makes them shinier with cutting edge technology - but the new industry which came to prominence does the opposite: it creates cutting edge experiences on technology with output resembling very old devices. Pokemon came out on Gameboy many years after it launched; and when the Gameboy launched, it already resembled very old technology (colour LCD screens were already around a decade old by the time the Gameboy came out).
That said, the AAA industry is shrinking, while the small studio industry is growing. The Switch doesn't need it to thrive and therefore doesn't need to go anywhere for quite a long while yet. The Switch-level hardware will be viable for at least another decade because most studios won't be making games that require anything greater.
Even if Nintendo Switch 2 comes out in 2021, mostly every game on it will be doable on the Switch 1, and Switch 1 wouldn't need to die any time soon - as it could continue its existence as a lower-end model - kind of like the iPad Mini 2 did for years after its release. I think next gen they maintain Switch Lite (1st gen) while phasing out the gen 1 Switch hybrid, and maybe have a gen 2 economy model Switch TV form factor. That way, it would make it a lot cheaper to port higher end games to a Nintendo platform - although, I still expect that the vast majority of Switch 2 games would be Switch 1 games as well, and I'd guess Nintendo would do both consoles if possible (since it would be possible and feasible if they support both gens). I'm a big fan of Nintendo expanding the form factors and perhaps evolving generations to be more like Smart devices, even though I'd be sticking to the highest end hybrid model, exclusively.
I describe myself as a little dose of toxic masculinity.
