How does this handle changing passwords? How can I know from the master secret that xyz.com is on the 4th password?
You can specify password length if it gets too long and it's character set provides symbols, numbers and letters in it.
>> How does this handle changing passwords?
It has a renewal mechanism to switch to a new password.
>> How can I know from the master secret that xyz.com is on the 4th password?
Can you explain more about what you mean?
So then there has to be metadata to list the site domain, username, which generation of password, which characters are allowed or disallowed, length, KDF difficulty, etc? Where is that information stored?
What I'm getting at is with a brain wallet I only need to remember my secret and know the algorithm used to generate the key. With this it seems like you need a database to store more information, and without it, it's difficult to get your passwords back.