Standarizing ECC seed, HD Wallets and WebID

The bitcoin block chain has a common function where you can derive a key
pair from a seed, and then use either the public or private key to derive
multiple addresses.

It is thus possible to standardize a way to give every WebID a unique
bitcoin address based on a private key, while only knowing the
corresponding seed public key.

This is a very useful feature on the web which would allow, for example a
server to issue deposit addresses to any user with a URI, and the key
material will never have to live on the server.

The only part that needs standardization is how to hash the URI and stuff
it into the 124 bit HD wallet index.  The suggested method is take SHA3 and
get the first bits.

I think this would be a super useful one page spec, and I hope to code this
up.

Let me know if there's more interest.