So I bought a Xunlong Orange Pi Zero. I tend to accumulate these boards, as one does.
It's a cheap small ARM board (badly) targeting Linux. What maybe sets it apart is that it uses the cheap and nasty H2+ chip and is quite small at under 50 x 50 mm. It should also have fairly low power draw.
I'll see what else the specs reveal and how this works.
Mine should be the 512 MB one. Looks like the SPI ROM is populated on this one.
I'm probably expecting this to run some small function somewhere, possibly with some Go program or stock servers. Perhaps it could collect MQTT messages and serve logs and graphs.