worth noting that Pinephone does boot against unpatched mainline (i.e. kernel.org) kernel. it’ll boot to a DE with graphics and touch working, but you lose WiFi/bluetooth, inherit some quirks with the backlight, proximity sensor, etc. no idea about the modem or audio.
as a NixOS-on-Pinephone user i 100% support funding upstreaming efforts 😉 that’s the type of thing which can have really broad reach. you’d never know it unless you were specifically looking for it, but we’ve also got people maintaining those OpenEmbedded musl+systemd patches for our distro (along with way too many other non-musl systemd patches: like you point out, it’s just not the type of thing that gets cleaned up without some focused effort like this).