There was a talk right after ours about LTO! I only half paid attention to it because I was catching up on the chat, but it sounds like Google is doing kernel LTO in prod for their internal systems (and maybe also for Android and CrOS?):

https://linuxplumbersconf.org/event/7/contributions/798/ (slide link at the bottom)

https://youtu.be/FFjV9f_Ub9o?t=3844