I looked into this a bit more, and it appears that there's little point to 
giving the user an option to clone or not clone when copying files, as the 
cloning (or not cloning) can occur anyway.

We plan to release a coreutils version soon and to change the default to clone 
after the release. For Emacs master the next release is far away, so there is 
plenty of time to try out the FICLONE performance improvement. I installed the 
attached two patches and am marking this bug report as done.

The second patch merely updates the documentation to discuss the issue; it is 
logically independent of the first patch, since the issue can occur both with 
and without the first patch.