Blizzard Entertainment recently announced the Purified Black Egg from the Badlands quest series will be continued through the Legendary Rogue dagger quests, and the purified black whelp is now a grown prince named Wrathion.
The Legendary Fangs of the Father questline is not yet available in PTR 4.3 build v14732. As a matter of fact, only the Caverns of Time: End Time heroic dungeon is available for testing. Well of Eternity and Hour of Twilight are still missing and to be available at a later time.
However, we can already see two crumbs from the Fangs of the Father questline.
The hatched Purified Black Egg can be found at the basement of Ravenholdt Manor. I compared the basement in live servers and in the current PTR build. Definitely a change.
A new NPC is now at the cave leading to Ravenholdt Manor. He is a red dragon disguised as a human. He’s named Mostrasz (The Wyrmrest Accord). Thus, it’s pretty much a given that the Fangs of the Father are tied to the Wyrmrest Temple in Dragonblight and the Dragon Soul raid. I couldn’t find Prince Wrathion, but he might likely be phased on top of where the egg can be found — considering there’s not a lot of space inside the Ravenholdt Manor.