Yeah, pretty sure Sylphlands is a placeholder area for whenever Ramuh is introduced. That might not be until patch 2.2 though. It's a huge area so I'm assuming there's going to be a pretty decent sized story arc there.

Another small area that wasn't mentioned was Proud Creek, northeast of Fallgourd Float. Currently it's only used for some Hunting Log mobs though. There's an Ixali camp and a bunch of Dullahans in the area.