Assuming this is not some kind of bug, I can see a couple issues with it in a PvP game with sieges and stuff!? Anyway, it will be tweaked a million times before launch.
PS If I remember the recent livestream well (?), devs might even enable them to fly while stealthed, but don't take my word for that!
Comments
Important detail is that video demonstrates greatly increased height/depth range of new maps - if you remember - the old "canyons" were quite shallow, and this is just first degree of improvement, devs said that now they have tech to put pieces of map such as this one atop another, increasing height/depth even further.
Namely, lots of people were complaining, for years, about maps being monotonously "flat". Also, we have caves now - another thing that used to be limited by some kind of Unity (game engine) feature.