[meltedcapacitor]

Are these vendor kernels good enough to run some sort of hypervisor and pass through devices at the lowest possible level to (updatable) guest kernel(s)?

The idea here would be to run things like the TCP stack, USB from the lowest proxy-able level the in USB stack, etc in the guest kernel(s), as well as the entire application level, so as to reduce exposure to vendor kernel bugs and feature freeze leaving it only with minimal SOC-specific nitty gritty. For GPIO the vendor kernel could be used as a PRU of sort, passing messages to the guest kernel for actual processing.

Then the vendor kernel is just treated as a BIOS/blob getting in the way as little as practicable, it's very ugly but would allow using all these boards, also same method could possibly be used to recycle obsolete android phones.