So typically an initramfs /init script will end with something like
exec switch_root /newroot /sbin/init
effectively replacing itself with systemd or whatever floats your boat. But what would happen if you fork prior to this? Will the new init system still be the parent of the forked process or will it be a zombie? In case of systemd, will a child process created before systemd starts create "bookkeeping problems" or have other unforeseen side effects?
Edit: Was asked in a comment for example code. Can't really see how that would change the principles behind the answer, but sure:
tail -f /dev/urandom & exec switch_root /newroot /sbin/init