This update will allow you to add cash to your Battle.NET balance which will then allow you to exchange that balance for in-house funds which in turn will allow you to purchase items for your characters to use inside the game. Battle.NET have updated their news feed with an alert that reads as follows:
"While we understand that this creates an extra step for players during the login process, we believe this added layer of account protection will help foster a safer auction house environment for all of our players." - Battle.NET
This update will have separate sections which include hardcore-only auctions, auctions for gold-only (as we've seen already), and normal real-money auctions. We'll be following this ecosystem closely to see what real cash money does to the world of Diablo this time around. Stay tuned!