That's 1980s-90s thinking. Nobody is making proprietary BSD forks any more and new kernels probably have no chance of reaching production anyway so worrying about proprietary forks is irrelevant.
The most recent and most used fork for freebsd is for the ps4
https://en.wikipedia.org/wiki/PlayStation_4_system_software
The most recent and most used fork for freebsd is for the ps4
https://en.wikipedia.org/wiki/PlayStation_4_system_software