Hear me out. I know a bunch of you feel like special snowflakes who earned your Naxx drakes and don't want anyone to have them anymore. But the Plagued Proto Drake being available on the BMAH and (assuming the Black has been spotted in the same way) means there's no reason for them to not be associated with the achievements anymore. The old ZG mounts? Sure, let those be unique to the black market because that version of ZG doesn't exist anymore. But the fact that anyone can get a mount that shouldn't exist anymore with gold means that if the original way to get the mounts was still in the game, it should continue to provide the reward.
Those of you who were good enough to get the Naxx drakes back in the day have one, two, sometimes even three titles depending how often you ran it (Undying, Immortal, and Conqueror of Naxxramas for the really good ones) that all show off what you did, all of which are more prestigious than the drakes that can now be bought for a lump sum of gold.
Hell, some folks are reporting the Ulduar drakes being available on the BMAH, and those are just as easy to get as the Glory of the Raider achieve is (assuming nobody sucks to Disarmed). And those drakes are still very much available, and have been since forever. Just the same way, nobody's taking away your Death's Demise, Herald of the Titans, or Conqueror of Ulduar achievements away (in the case of Herald, you have to do the exact same thing now that you did then, and the other two are long gone).
Titles are enough, especially if the other reward in question that you're clinging to is just easily bought on the BMAH for those who wait long enough.