If Nintendo have learned their lesson they will not try and artificially inflate the Switches life, nor will they wait til it dies before introducing a successor. This will lead to second wave of sorts. Switch will continue to sell based off the casual market & people looking for a secondary console picking it up for its 5 or 8 major system sellers, meanwhile they should move their core audience onto next gen. I've been saying for a long time Switch 2 should come sooner than later (Fall 2021) and have period of cross gen.
-Soft 1st party launch with 1 or 2 big exclusive (i.e Metroid 4/Splatoon3/Starfox Reboot) targeted at their core audience.
-Cross generational launch titles which greatly benefit from the new hardware i.e Breath of the Wild 2/Bayonetta 3. (Outside of already announced games the OG Switch only receives low key, casual orientated titles which don't beg new hardware).
-Major 3rd party Support not available on OG Switch. FFVII, Assassins Creed etc. The key here is that PS4/X1 will still be receiving support into 2022. Switch 2 launching before or around could gather major support. Unlike the Wii U it would be a proven concept, have scalable engine support from the likes Epic, have the portable USP and have hadware that would show great promise towards the future (DLSS) and alignment with key PS5/SX features as oppose to the PowerPC mistake Nintendo made with Wii U.
On this logic I also think Switch 2 should be a premium 399 and live alongside OG Switch which would be an evergreen 199 family box.