What?! Almost every major server and desktop Linux distribution ships a kernel full of patches, which are absolutely forks. That’s before we start getting into the crazy town of the embedded world. Clearly the software can be forked. The question is whether the community can - and that is yet to be seen.
All those "forks" are dependent on regularly rebasing their patch sets on top of mainline (or they never get updated and lose what semblance of support they had once the SoC they were made for reaches EoL), so they're pretty much irrelevant to this conversation. We have seen no indication that it's feasible for anyone to hard-fork the kernel and continue development in a way that's independent from what we today call "mainline".
