It seems a number of various vendors have come up with a formula:
* Use bitpay (or other bank partner) as a processor, vendor gets paid in USD/fiat.
* Refunds only in store credit in fiat (to protect vendor from fraud).
As to who would use it? Impossible to say without an experiment. Perhaps bitpay would share some backend data on use with a potential partner.
Personally I often pay with bitcoin on Steam and with Newegg.
Edit: Naturally there are likely to be some customer service headaches, and training for service people. For instance when btc fee is set low; but bitpay does a good job of notifying the customer and explaining the delays. Bitcoin in general is still a little rough around the edges.