However, Motorola/Lenovo seems the most logical partner, they were previously in the Android One program (which was sort of the successor to the Nexus line).
That would be interesting. I have long wished that Sony phones would allow re-locking the bootloader to an OS signed with my own keys.
Some of their Xperia Compact models have been excellent, but they haven't been making them like that in recent years. Dare I hope for a return of their truly compact flagship phones and GrapheneOS support?
As far as I'm aware, their flagship Xperia phones do support bootloader re-locking [1]. The problem is they haven't fulfilled GrapheneOS's other requirements: https://grapheneos.org/faq#future-devices
I use Sailfish on an Xperia 10 mod. III. Unfortunately the only Xperia models which support the full Sailfish w/Android compatibility are the way too long ones. I intensely dislike long phones. I miss my old Jolla phone (they're the maker of Sailfish), it was perfect but developed a technical problem after many years. The Xperia is clumsy when compared to the Jolla phone. Glass surfaces back and front (who thought that was a good idea? Glass is slippery, and glass breaks), sometimes slips from my hand, or wherever I put it if it's not 100% flat. Glass..well, you get the idea what happens then..