It seems like really threading the needle to get someone
*Enthusiastic about streaming PS5 games to a portable device.
*Unwilling/unsatisfied with existing gamepad accessories for phones/tablets to the point where they'd rather wait and spend significantly more on a single-function device
*Unenthusiastic enough about portable gaming to not get something more fully-featured that offers more when network is unavailable.
not more then the PSVR, with a fraction of the cost. Its simply not a huge risk.
The hardware is readily available and does not need much expensive R&D,
it doesn't need cutting edge hardware thats hard to source.
You picked those points, but ignore one that tied them together:
already being invested in the platform. How many don't move from apple,
because they have already bought their apps there.
How many only want portable PC gaming if it supports Steam.
If its "ok, steamdeck looks cool, but buying all of those games again and paying 450€" or "180€ and just paying my PS4/5 library" ... yeah, i do see it as a "doesn't hurt and expands the brand" kinda offering.
From a PS walled garden kinda perspective it could be a valid option.
If definitely is not something for somebody thats not already invested in that platform.
But since you can play your bought PS4 games on PS5, there are people with potentially hundreds of games they bought over the last decade.
And from my perspective, i rarely play my switch outside of my home, but often portable, and when i play it outside, im at university (wifi), at a friends place (wifi) or on the train (no wifi ... or at least, not a good one). 2/3 of those would work perfectly fine for game streaming.
Lets argue from a different perspective: If nintendo does not support 99% of their digital games with the next platform, im instantly gonna stop buying indie games and multiplat games there.
for me that means they are not as commited to the eco system as they want me to be with my purchases, and then im moving to PC. as it stands, Switch is way more confortable, but loosing my library when moving to the next switch would mean, my library is stuck on a console that will not live 10 years from now, and will be hard to find replacement for.
The same can be sad for sony: they are not able to provide portable gaming as nintendo and steam are, so their next best bet is streaming (and they are having that), so why not also have a dedicated cheap solution. (the benefits are obvious, doesn't drain the battery of your communication device, better ergonomics, bigger screen, better battery life...).
Again, it only works if they are clear in the marketing and keep the price low.
Its not about serving a new audience, its keeping their eco system attraktive by having options for their existing audience to not switch to a different walled garden.