The more I think about it, the more it makes sense:
Switch 2 will most certainly be a handheld hybrid again. The PS4 and Switch both benefitted greatly in a sort of symbiotic relationship at the low-end/indie side of the market, getting all sorts of games well past the end of their 5-year cycle. To this day, games are launching on PS4 and Switch and skipping the current-gen consoles (sometimes getting a later release).
Switch 2, Steam Deck, and presumably Sony Portable will be in the same ballpark power-wise, at least as close as the Switch is to the PS4. Original Switch will still be around as a budget option for a few years, so that's a huge market incentive for companies to put all their games "on the handhelds".
Sony is pretty good at making mass-market consoles with tons of third party games. Entering the same space as Switch 2 and Steam Deck means a lot of games getting ported across all three.
The big question is: physical copies or not? Chip tech is advanced enough to do "cartridges", which is how they handled Vita. Fast read speed cartridges would help match the SSD speeds of the PS5 (and a handheld should be speedy anyway).
I can't imagine it wouldn't be Digital Only.
It is definitely possible though.
The Steam Deck hit 350 quidbucks a couple of years ago with tech that put it roughly in line performance wise with the XSS/X for it's target resolution of 800p, and has allowed it to play basically everything that's come out and not been an unoptimised mess on PC so far this gen, with MS Studio games in particular working really well on it, especially after a few patches and some fiddling with settings.
So if Sony can aim for the same price tag as the PS5Digital, with those extra couple of years of tech improvements and better economy of scale, targeting 1080p on a handheld, a quarter of PS5's target, thus requiring only a quarter of the power, should be entirely possible.
The only real issue would be the TDP, because the PS5 is a thirsty cow when it comes to power, and the CPU likely couldn't be as well cooled.
However a patch for the more intensive games to limit frame rates and force a quarter rendering would most likely be relatively easy, especially if they keep the architecture as close as possible and the RAM the same but for amount. Hell, it could well be easier than porting XSX to XSS, since Xbox really ballsed up with how different those two systems are internally.
Frankly, there's probably never been a better time to try this. Like you say, we have numerous low spec systems this gen that will keep developers from going jam with game designs so 99% of games will be able to scale, mobile and energy efficient computing tech is the most efficient it has ever been and much more cost effective to make than high end tech, and with the PS5Pro on the horizon they'll already be providing tools and asking devs to provide new hardware settings for their games going forwards, including patching older titles. They could easily add a low settings tool pack for a portable at the same time as the PS5Pro's high ones.
But like I say, don't give me hope. A PS5P would be a day 1 purchase for me, and I've already had my heart broken once with that portal Gamepad piece of shite.