I'm pondering your idea... I definitely like the idea (as I wait for my BTC to post to cryptsy) ... But I think you would need a certain amount of each currency to exchange with yourself... But if you had it... why not? What if Darksend could add a second conversion value for a transaction, allowing any other currency to "piggyback" on it... Imagine the pool having not just Darkcoins, but BTC, LTC, DOGE, etc all in each transaction. More layers of concealment... But you WOULD have to make sure that the current pool could support your transaction... and how could you make sure that the conversion wasn't being gamed? You wouldn't want to use a fixed rate, that would be self-defeating.... Hmmm....
BTC/Altcoin -> Counterparty -> DRK
DarkSend that shit
Darksend that shit again (why not?)
DRK -> Counterparty -> BTC/Altcoin
Basically, use DRK for the DarkBank and then just withdraw it as you need it into the other cryptos. That's my plan, anyway.
I should add, the whole point of Dark is that the mixing is decentralized. In order to accomplish what you and the other guy are pondering, you must trust 3rd parties again, which isn't optimal.