Commerce Vocabulary

I've been working on a credit system for the web ( webcredits.org ) for a
while and I thought I would reuse the the commerce vocabulary, in
particular the Transfer class.

https://payswarm.com/vocabs/commerce#Transfer

However having thought about it for some time I think perhaps this is
better modelled in its own class.  Maybe something like "Credit" like a
credit system of IOUs that can model both an IOU and individual credits (eg
in a game or a ledger).

The mandatory fields would be:

destination -- who has the credits
amount -- how many
currency -- which currency

This would be enough to create a ledger (as per my post yesterday).

To specifically show who the IOU was from (either by way of log or
transaction)

source -- who the credit came from

Optionally two other fields could be useful

time -- for a timestamp (though systems like bitcoin only add a timestamp
after accepted)
comment -- a note explaining that entry

Im thinking of updating the web credits spec
http://www.w3.org/community/webpayments/wiki/Web_Credits along these lines.

Do you think it would be possible to add a Credit entry to the commerce
vocab?