steemit is not globally accepted either. it only has value inside the steemit network. key here is the easy exchangeability trough atomic swaps or decentralized exchanges. Bancor introduced the concept of automated market makers via smart contracts that guarantee liquidity for the supported asset. Lots of the ICO projects that focus on usability implement a mobile wallet with a build in decentralized exchange so that you can flip your coin in the one you need transparently at the point of sale without thinking about it. Like today you would have to pay something in USD and the price is converted for you to BTC at the time the payment is made. The merchant would receive the BTC and convert it back to USD at his bank or in his wallet.