The current proposed patch allocates the following psql \d commands:
\dw show foreign-data wrappers
\dr show foreign servers
\dm show user mappings
One might object that this allocates valuable letters for infrequently
used functionality.
In an idle second I thought, how about F for "foreign", but of course
\dF* is already used for full-text search. We could overload the F, but
it might be weird.
Other ideas?