I think many have been doing that already since many companies have already allowed cryptocurrencies to be used that way, or a select few of them for that matter. I think, as more and more coins would be accepted by more companies, especially the trusted ones to be used as a payment for goods and services that would open new doors for the horizons of cryptocurrencies. However, for now, it is limited because there still a lot of considerations that companies think of, since we can't hide the fact that cryptocurrencies, in terms of its value, changes in a blink. So, as a company that needs a return for its capital, it would be too difficult to just accept and accept cryptocurrencies knowing how it can be unreliable.
The real shift for me would be for merchants to start ditching those payment processors that actually doesn't do anything other than make a Bitcoin-fiat gateway. I'd really like to see more "Bitcoin accepted here" signs to mean that merchants are actually using their own Bitcoin wallets, and not forcing customers to pay using something like Bitpay, where they've to pay fees anyway (not to mention the inability now to use RBF or even set reasonable fees, as Bitpay's network insists you pay exorbitant miner fees).
With LN really smoothening out its rough edges too, there could be added incentive. Not sure 2019's the year for that though.