"Initially browsers use the temporary IPV6 address. After a while they start consistently using the permanent one."

This is the most troubling aspect to me. The process of enabling the random ipv6 address would be:

1.Click the "enable" checkbox

2. Check if it's working. (initially, it does)

3. Forget about it for the next 12 months

Somewhere between Step 2 and Step 3, the feature spontaneously turns off and the ipv6 address is leaked, and the user is none the wiser.