Trustless trading of bitcoin for bts/bitassets could be a killer feature for bitshares. I'm sure that it's already been though of already but it seems possible to create and enforce contracts which depend on conditions within the bitcoin blockchain being met. For a very basic example, to make a trade of 1 btc for 278 bitUSD, a contract could transfer 278 bitUSD to a specified user when a specific bitcoin address contains 1 btc with at least 1 confirmation or else expire after 1 day. Is anybody working on this at the moment?