I think there are good thoughts on this matter in the middle of Solving the Cryptocurrency Liquidation Problem section of Steem Whitepaper. Accepting a volatile currency introduces significant accounting overhead for merchants but eventually merchants should accept any currency if it increases their sales (assuming there's a way to deal with volatility). The number of bitcoin users grows 10 times each 2-3 years so yes, that is a question of time.
P.S. Seems like Steem discussion is limited to 6 levels as I'm not able to respond to your latest post so I'm replying to this one.
Well said. We integrate with Coinbase and BitPay to try and eleviate any volatility concerns but I think, ultimately, it comes down to not doing anything unless your customers are asking you for it. More unfamiliar payment options could lead to more support costs. Moral of the story: get out there and bug your favorite merchants until they accept bitcoin. :)