"none of these are going to be supported by upstream in the way a cheap Intel or AMD desktop will be"

Going big-name doesn't even help you here. It's the same story with Nvidia's Jetson platforms; they show up, then within 2-3 years they're abandonware, trapped on an ancient kernel and EOL Ubuntu distro.

You can't build a product on this kind of support timeline.

For what it’s worth, Jetson at least has documentation, front ported / maintained patches, and some effort to upstream. It’s possible with only moderate effort and no extensive non-OEM source modification to have an Orin NX running an OpenEmbedded based system using the OE4T recipes and a modern kernel, for example, something that isn’t really possible on most random label SBCs.

Yup, I'm working a lot with Jetsons, and having the Orin NX on 22.04 is quite limiting sometimes, even with the most basic things. I got a random USB Wi-Fi dongle for it, and nope! Not supported in kernel 5.15, now have fun figuring out what to do with it.