Waiting until 2022/2023 will be a disaster. IMO Nintendo knows this 100%, they're not going to wait that long. There is no Game Boy/DS second product line for Nintendo to fall back on if the "console" fails either. It's far too risky to do things that way. The upgrade cycle has to change.
Even look at their software by the end of 2019 Nintendo will have used up Mario 3D, Zelda, Pokemon, Pokemon Lets Go, Animal Crossing, Splatoon, Mario Kart, Smash Brothers, Luigi's Mansion, probably Metroid, Fire Emblem ... they can make sequels to these IP but the hardware boost is going to be nowhere near the same because much of the fanbase will own a Switch already for the pre-existing game.
With what new IP are they going to sell the Switch with for 2020, 2021, and 2022? It will be a disaster with declining sales every year and no, some little New 3DS style upgrade or even Switch Mini is not going to be enough for Nintendo to maintain a high level of sales.
Then Nintendo are shit out of luck regardless ? The console cycle just simply needs a hard reset irrespective of the next generation system featuring BC or not and that's the way it will remain because if their only way of maintaining higher hardware sales is through selling new iterations of their franchises advertising the capabilities of their next generation system then it won't mean much whether or not they adopt your so called "PC model" since they only did it in name only ...
After all, aside from releasing a more expensive model to appease the 3rd party developers what are the other advantages your model offers compared to existing home consoles who also offer upgraded systems as well ? Should Nintendo titles also adopt a continuously updating development baseline or should they also stick to a hard baseline target and change it as if there was a new upcoming generation just like how every other console manufacturer did so far ?