Blizzard announced this today, you may have seen a quite comical video posted by our beloved monk-admin. :) Below is the full article @battle.net:
The Collector's edition is not available yet but if you're shooting for digital or digital deluxe you can get it today! With the prepurchase your account that is enabled with the new expansion will recieve a coin on the character select page where you can use it to boost one of your existing characters or create an entirely new one!
Here is a how to video incase you're too lazy to scroll through the article: