Proto-Drake and Rare Mounts in CataclysmI don't know of any other rare drakes they could be talking about except the one in Utgarde Pinnacle which is already a rare drop. Looking at the question this answers, the person was asking about the Red Proto-Drake from Glory of the Hero.
This is all tentative and could change, but we don't really have a problem with protodrake farming. What we will probably do with really unusual mounts like Mimiron's Head and Invincible is make them a rare drop. The 100% drop rate won't make sense when you can overpower the content.
If you want to overpower the content for a drake though, go for it. Players who did it "legit" had the benefit of having the achievement and mount earlier than anyone else. The most prestigious mounts will change in Cataclysm. (Source)
So it seems that the red one at least will still be available after the expansion.
This also implies that Blizz may be leaving the current raid achievement drakes. We'll have to see about that, though. It's less likely but still a possibility.