I haven't tried 6 yet.
It appears any time you ride the rocketway. It's not a quest. More like a flight path made by goblins... with rockets that you can jump off of. Just head vaguely NorthEast from Ogrimmar and you'll find it. The path looks like a paved road. Follow the road and you'll find a number of rocket masters that let you ride the rockets as quick transport.
When you're riding a rocket, the eject button appears on the bottom left side of the screen just above your left actionbar. It seems to be a unique added button and isn't part of any other button set as far as I can tell.
I'm not sure how many of these things were snuck in for Cata. I'll keep an eye out.
Edit:
This rocketway:
http://www.wowpedia.org/Rocketway