And that may well happen, but you will still get plenty of content to play. It's not like Switch Pro will show up and OG Switch will suddenly get like only 10 games a year. Try several hundred, try probably more than you could ever spend money on or have time to play.
As a business I can't run my business and put it at risk and also hold back my hardware sales just because of this group of consumer. You have to be reasonable.
Nintendo is already making a fairly large sacrifice in giving you one system that can play basically all their content instead of asking for two (which worked out to like over $500 US), they owe it to themselves to have higher hardware sales and more models will provide that, but they have to be significant upgrades, consumers are not stupid and are not going to go crazy over little dinky New 3DS style upgrades (case in point -- none of the 3DS revisions caused any kind of large boost in fiscal year sales for that product).
A hybrid between the PC setup and how Apple does business is what's best for Nintendo. It will mitigate risks that come from hardware transitions (that historically have blown up in Nintendo's face half the time) and it will prevent against things like hardware shipment collapse after year 3-4 of every hardware cycle that plagues almost all Nintendo systems, even the successful ones. There's only so many Nintendo IP, and you end up using them up basically by the end of that 3rd year, then you have problems selling hardware. Switch is going to have that same problem.
Getting only 3 years before non-Nintendo games turn to shit and you're left with only the handful or less of worthwhile games Nintendo release per year is horrible for the consumer, you're screwing over what will then be over 50 million paying customers.
Leave it up to the dev. Likely speaking what you'll more likely get are games like Resident Evil 2 Remake that simply cannot run on the OG Switch that are Switch Pro-only ... but really you wouldn't have gotten that game on the OG Switch anyway, so what exactly have you lost? Nothing. If anything you've gained something because that game will be there waiting for you, whenever you feel like you want to upgrade.
Just like today I can buy a new PC GPU and I know there are new games waiting for me to play that my GPU can't run. And that's great, that's power to the consumer, I choose when I want to move up, it's not dictated to me by a company deadline like I'm a 10 year old that needs to beg my parents to buy me my video games.