The main challenge there as I understand it is that the Steem ecosystem as a whole is intended to be decentralized. Being able to directly withdraw from steemit would require a central authority doing the trades from Steem -> Other Crypto -> Fiat.
Someone could start up a fiat exchange directly with steem - but that would require fairly significant risk, overhead and couldn't expand globally all that easily.
RE: Will we ever be able to withdraw our money directly through the Steemit platform?