Two huge things:
First off: what the hell is Thal'dranath? They didn't mention it when talking about the zones of the Broken Isles. It could easily be confused with Val'sharah, but one of them is definitely the area where Malfurion learned to druid and the other...
Well, the name seems very elvish. It's connected to the Broken Shore, but I don't think we know the backstory really at all.
Now, here's the grain of salt time - Farahlon was clearly present on the map of Draenor, and we never got that zone, so this could wind up being nothing. But I hope that Blizzard has learned the lesson that anything that's even hinted at better show up or you'll risk disappointing a lot of people.
I also hope they learned the lesson in Warlords that players really, really don't like these "small scale" expansions, and we want them to expand the world significantly over the course of our time there.
Second big thing:
Acherus! The Ebon Hold is apparently heading to the Broken Isles. So it seems likely that there won't be a new order, but that Death Knight players will go on to lead the Knights of the Ebon Blade. Acherus obviously has the same advantage that Dalaran does that it can go to where the action is - in fact, it's probably a lot easier to do so, as Acherus was built specifically to float and move, whereas Dalaran was an (relatively) ordinary city torn out of the ground with arcane magic.
It looks like Acherus is on its own tiny archipelago, which, if there's any justice in this world, is a blighted land crawling with skeletons and ghouls.