I found documentation about importing a bitcoin private key into bitshares
http://docs.bitshares.org/muse/migration/howto-exporting-wallet-clients.html
If it is possible to have the same private key for both a bitcoin account and a bitshares account could you then use your bitshares account to sign bitcoin transactions?
I'm contemplating the concept of using a bitshares account to sign bitcoin transactions
You could also broadcast a bitcoin transaction by putting it in the memo and sending it to a specific account.
Which would open up payment channels/lightning network
imagine 2 separate BTS accounts opening a bitcoin payment channel with each other
and both re signing a new 2 of 2 transaction everytime a witness updates a feed price.
You could have a bitcoin payment channel contract between 2 bts account that would promise one of them $100 of bitcoin and the other $100 loan of bitcoin.
I have also posted this in the bitshares forum: https://bitsharestalk.org/index.php/topic,24969.0.html