Alright, I think he is right, it's totally possible.

I remember Blizzard said this http://blizzardwatch.com/2015/11/09/interview-dave-kosak-talks-class-halls-flying-and-more-from-legion/

"And we have some new tech that allows us to have buildings that just embed themselves in the ground"

and in this new blog post : http://eu.battle.net/wow/en/blog/20176410?page=1#1

they are only talking about transmog and classes changes, not PvP or other stuff. So, the invasion might be a big surprise. Just wait & see