This is kinda cool and gets gets used every so often, but much more useful would be the reverse.
Cleaning up files in the process of being created before they are renamed() into place is a pain. If you could create a new filesystem fd in the unlinked state first, and then link it into the filesystem once it was ready, all the temp file and unlink-on-error nonsense could be done away with.
newfd() would have to take a path to associate the fd with a particular filesystem, like statvfs(), but that's easy.
A lot of newbie programmer errors where a partially-written file is put into place over the existing file would be eliminated too. I bet this could have saved a lot of trouble over the years.
Kinda late to be adding calls like this though. 30+ years late.