Considering the problems with /dev/{stdin,stdout,stderr,tty} and the
   fact that fdesc requires the union filesystem to be useful, I propose
   that it be changed to only supply /dev/fd/<filed-descriptor> and be
   mounted on /dev/fd.

First of all, it does not use unionfs.  It's normally mounted only with 
MNT_UNION option, which does a shallow union.

I object (strongly) to simply castrating it.  It's fairly trivial to fix,
and someone should just do it.