Ethereals are definitely a big part of an upcoming TWW patch. Even if the new models are meant for a playable race there's no reason they are all in the TWW files so early.
I really don't think we're going to get Karesh until Midnight. It works very well as both the starting zone for playable Ethereals and the final area to go to at the end of the expansion to deal with Dimensius.
Something I hadn't considered until writing this... I believe they said Xal persists through the whole saga. But what role would she even have in TLT, especially if we defeat her master and the antagonists shift to Iridikron and Bad Keepers/Titans?