And that's cool.
First of all, it's added a whole extra layer of meaning to old content. Suddenly we can retrospectively understand what those crystal pylons were all about, and just why the soil in Un'Goro can grow things other soil can't.
Secondly, it's the first time that the inability to fly in the old world is a positive boon. Now, in an out of game way, we know that this part was added to Un'Goro with Wrath, but as we could never get up there to find out, it could, in an in game sort of way, have been there all along.
And that is intriguing, isn't it? What could have been above (or below) familiar zones all this time? What secrets of the past are lurking behind the veneer of zones we thing we know well?
I really hope that this little glimpse into the unknown parts of well-known zones isn't a one-off, but something Blizzard chooses to intrigue us with again in the future…
(That said, it was bizarre getting a zone's quests completion achievement in another zone completely – and on another continent, too.)