Luigi Dude is depressing me with the 20-30 years comment. I'm currently playing a PS2 game that is now over 20 years old. Will I be playing an equivalent of that when I'm in my 60s? Hmmmm.
Though we don't need to go 20 years. The Switch is 8 years old which means that the 3DS ceased to be a current system 8 years ago. If I want to play a 3DS game today that I don't already own I need to find a used cart. I can't buy it from the digital store anymore and Nintendo cut that cord really quick. Now with the Switch 2 being backwards compatible that is not likely going to happen with the Switch 1. It seems Nintendo is now finally using one store and account that will cross multiple generations. But it wasn't always that way and that was a good reason to support physical games on the Switch.
Even though it's not currently happening, I wouldn't be surprised if by the end of the Switch 2's lifespan, DS, Wii and 3DS games will all be added to NSO. I mean Wii games are guaranteed to happen since we already know from Mario 3D All-Stars that Nintendo has a working Wii emulator, similar to how that same collection showed they had a Gamecube emulator that will now be used on the Switch 2.
DS games should also be a guarantee since third parties like Capcom and Konami have already put out collections in recent years that have some of their DS games running on the Switch with the touchscreen parts reworked. I imagine Nintendo already has the same ready to go for most of their DS collection. The 3DS should be even easier since most of Nintendo's own games stopped using touchscreen by then.
So by the end of the Switch 2's life, the system will have access to almost Nintendo's entire category of both home and handheld systems through NSO, and all the Switch 1 titles will still be buyable from the eShop. And since Nintendo will keep building on the Switch, for Nintendo's own published titles, the future will be looking pretty good with easy access to the vast majority of their own published titles at least for the coming decades.