Wired:

On Tuesday, Amazon handed down to its customer service department a policy change that no longer allows people to call in and change account settings, such as credit cards or email addresses associated with its user accounts. […] We discovered Amazon’s policy change on Tuesday after we failed to replicate the exploits used on Honan this weekend. Amazon declined comment on the security hole on Monday, and has since failed to return repeated phone calls from Wired about the vulnerability.

It seems to be in practice already. A good thing the hack happened on a known journalist, not sure this would have had the same impact.