As an idea, a scribe should be able to make a Scroll of Temporary Entitlement, that would be retroactively be available for each expansion, to allow you to give yourself any non-PvP title from that expansion for 1 hour. And then if you have some certain amount of Honor (or whatever the PvP currency is), you can take that scroll to the PvP equipment vendor, to get it upgraded to PvP titles.
And, yes, this would include not only titles retired from the game, but also “Slayer of Stupid, Incompetent and Disappointing Minions”.
If Blizzard really wants to put a modern spin on it, the removed titles would only be gainable with a 3 star scroll.
Just a thought, because sometimes I like to see the world burn.