It could be possible now that BTC Relay is up and running. That wasn't really an option when this DAO was being formed, but a future DAO could theoretically use this to store BTC as a backing value for their tokens on the Ethereum network and just utilize the contracts as a way to manage the organization while keeping all their funds in BTC. That would obviously be a bit more involved and that whole concept is still fairly experimental, but it is definitely a scenario that is on the table so to speak.