Blizzard can make authenticators a mandatory feature on all Battle.net accounts.
There are many pros and cons such a move would bring about. Let's examine the cons first since everyone likes to complain about stuff. The largest con would be that people would be required to have a physical piece of equipment specific to WoW and other Blizzard games. Some people would obviously not be okay with this and cancel their subscription, and others would not understand how to push a button and punch in numbers (I'm not kidding). There would be a large cry from people around the net, particularly people who enjoy scamming others out of gold and their accounts, but those are easily enough ignored.