I'd like to propose a BIP for a standard URI scheme to allow wallet
operators that implement instant exchange or pegging to other currencies,
cryptocurrencies or asset classes to allow for interoperable communications
of rates and other pertinent information.

The idea is to include in the wallet address as parameters information that
supplements the presentation of a proposed transaction.

For example, a wallet operator that instantly exchanges bitcoin to gold
would present a wallet address as follows:
bitcoin:1JohnxNT6jRzhu3H1wgVFbSGKmHP4EUjUV?currency=xau&rate=0.2084&expires=1458432000

Wherein:
:  the currency, cryptocurrency or asset that the transaction
will end up as encoded in ISO 4217 if applicable.
: the bitcoin to rate as dictated by receiving wallet
: unix timestamp of when the rate loses validity

This would allow the sending wallet the ability to present up-to-date
exchange rates. When, for example, a wallet operator that pegs to the USD
scans the address above, it would be able to present to the user the
following information:

1. USD to XAU rate
2. How much XAU will be received by the address
3. How long before the rates expires

Thoughts?


BTW, I've posted this to the bitcoin-dev mailing list.