No matter how well you design it you can't prevent government intervention at the exchanges that can cause unforeseen problems. If the bitfinex hack was the result of government regulations requiring the funds to be kept the way they were for the exchange to operator the same thing can happen to any currency stored on such an exchange for trading.
RE: Bitfinex, Blockchain Hacks, and Replay Attacks Oh My - All Things that Steem’s Technology is designed to prevent.