Something I'd be very interested in seeing summarized is the current state of fully open source software on SoCs and SBCs. I hate how common the situation described in the nVidia section where SoCs that require vendor kernels get abandoned on ancient software, so it would be very useful to know what SoCs are supported to a useful level by mainline kernels.
I feel like there are three tiers of support that most people would be interested in:
1. Usable for headless appliances (serial console or unaccelerated graphics, wired networking, storage, USB)
2. Usable for interactive use (accelerated graphics, WiFi/BT)
3. Fully supported (all major hardware works)