Implementing it is easy, but it might be a hard sell for the project because it creates a precedent.
We already have "help" (without slash) so I don't think it is a precedent.
The next question in that list is "PostgreSQL DESCRIBE TABLE", so why not implement "desc tablename;" as a synonym for "\d tablename"?
I must be honest to you, I create this small patch to see how is contribute do Postgres and to check how is reception on Postgres community.
That said, DESC[RIBE] is on my list for next patches but it is not a synonym to \d.
DESC[RIBE] must be a SQL command, very useful when you are not running psql. But let us discuss this on another thread ;-)
The question after that is "Show tables in PostgreSQL", so why not implement "show tablename;"? Well, this one is impossible because SHOW is already a SQL command that does something else, so that's already the end of that road to compatibility.
Didn't know about SHOW command. Are TABLES a reserved word?