We're working with a major Android OEM and it's going well so far. It's still in an early phase where they've assigned a small amount of resources to it to determine everything which needs to be done and then make the case for a much larger investment of resources. We expect that to happen and for it to go well.
All the same non user initiated calls to Mozilla and other endpoints. Run tcpdump to see them. (both TCP and UDP now) I run a command before I close internet applications and all outbound connections are logged in dmesg via netfilter. Be sure to also log all DNS queries on your firewall.
I have one with "Pixel Experience" and one with 'PixelOS". Both of which, by my understanding, are built on top of unofficial Lineage OS releases - but I might be way off base.
Pixel Experience was not based on LineageOS. And Pixel Experience is dead and unsupported now. While there is no official direct successor, EvolutionX offers a comparable feature set.