Just a follow-up for anyone developing this further. What do you think about using an existing link relation type for bitcoin? "payment" seems to be about right...
So a link might look like:
Relation Name: payment
o Description: indicates a resource where payment is accepted.
o Reference: [this document]
o Notes: this relation type registration did not indicate a
reference. Requested by Joshua Kinberg and Robert Sayre. It is
meant as a general way to facilitate acts of payment, and thus
this specification makes no assumptions on the type of payment or
transaction protocol. Examples may include a web page where
donations are accepted or where goods and services are available
for purchase. rel="payment" is not intended to initiate an
automated transaction. In Atom documents, a link element with a
rel="payment" attribute may exist at the feed/channel level and/or
the entry/item level. For example, a rel="payment" link at the
feed/channel level may point to a "tip jar" URI, whereas an entry/
item containing a book review may include a rel="payment" link
that points to the location where the book may be purchased
through an online retailer.