Indeed, this is great. All newsletter popups, cookie popups, "are you sure you want to leave" popups, give us feedback popups... They will all go on the top layer so your adblocker could hide it all at once.
That is the reason why the top layer will not be chosen
For that reason two dialogs will be opened in the same place. One on the top layer, and one on the layer below it.
Except if that happened, they just wouldn't use it.
They don't care about the 1% of users who will figure this out.
Wow, that would be great actually. Right now heuristics to block “please sign up for the newsletter” dialogs is difficult to do. But hopefully in the future we can just selectively allow access to top layer for certain domains.