But who is going to hold the bag?
Every merchant can opt to be a bag-holder
If wishes were horses, beggars might ride
A simple question begs to be asked, i.e. why merchants would want that in the first place? Are they in for charity or what? If they don't have economic interest in that (which in most cases boils down to pure profits), they won't do anything along these lines. More specifically, they will just increase their profit margins and will ask for hefty premiums to avoid getting caught by Bitcoin volatility (or choose to abandon Bitcoin altogether). Why the American dollar is universally accepted around the globe? Right, because it is as solid as rock
In that case, the merchants needs to use a third party payment processor such as Bitpay or Coinbase, which immediately converts the Bitcoins to USD or any other fiat currency of their choice. In this way, they can insulate themselves from the exchange rate fluctuations. I am not sure about the fee charged by these payment processors. I heard that it is around 1% (still better than the 1.8% charged by Visa/Master).