Just to test some waters here, do we think there is a market for peer-to-peer trading like bitcoin-otc (
http://bitcoin-otc.com/)? I checked their website but there is no altcoins in the 'otherthing' column, which presumably supports quite a number of currency units.
When I enter a buy order for bitcoin, paying 2% premium I might enter it as:
;;buy 1.0 BTC at "{mtgoxlast} * 1.02" USD "Can pay with PayPal, Dwolla, Serve, etc."
So there is no restriction against any other currency. I could today enter an order to pay for litecoin with bitcoin. The order I enter for that is:
;;buy 300 LTC at 1.0 BTC
or vice-versa:
;;buy 1.0 BTC at 300 LTC
What I'm suspecting is that you are looking for a dynamic price method, just like how "{mtgoxlast} * 1.02" will dynamically calculate the price based on "market" price. To provide that, the Gribble bot would need to be modified to become aware of the alt-coin exchanges. I'm not even sure how you would determine "market price", since unlike bitcoin there isn't one dominant marketplace for each alt coin, as far as I know. You could make an appeal to get at least some exchange quotes for some alts added to gribble. Or you could make your own bot (using the open source gribble code) and have a separate OTC channel.