I think they should add any mount or pet that you cant get ingame anymore. This way people still need to run content ingame to earn them and people still had enough time to be special with their mounts. I mean the Falcon was something you earned by giving them money. So if they can bring back that thing, then I see no reason to leave the PVP mounts exclusive..
In both cases its a mount that people wont be able to get anymore. And if that one reward that was giving as a thank you for subbing at that time can be given away for such a low amount of tomes then PVP ones should be too.