Whilst we are waiting for the BTS bond market:
Metaexchange is a great way to instantly get coins and take them to any other exchange to trade with. So why not allow users to post collateral in BTC to borrow altcoins to short sell them? Only issue is how to calculate how much collateral to require to control your risk. 2x collateral sounds reasonable to both sides.
If Voorhees announced this feature for shapeshift.io, it would be an instant hit. He could call it "Short some shitcoins at shapeshift!" I should copyright that.
And once the BTS bond market is running, maybe metaexchange could integrate that and operate as a frontend to the best blockchain loan offers.