Ha, abusing fork for asynchronous saves is clever. I hope they are aware of the following restriction:

After a fork() in a multithreaded program, the child can safely call only async-signal-safe functions (see signal-safety(7)) until such time as it calls execve(2).

Enabled async saves and it’s a gamechanger.
Is everyone getting the stutter when the save starts?

Very interesting FFF, I love the details about Linux support.