Maybe the price of the good should be in the local fiat currency but payments should be made with Bitcoin. So regardless of how the price of Bitcoin moves, the shop owners will not be affected.
Of course that's how it currently probably works in 90%+ of all cases - they very likely use Coingate/Bitpay and similar solutions or directly connect to an exchange.
However, if the economy really has the ambition to become "circular", eventually at least part of the coins should not be converted anymore. I can imagine scenarios where local merchants first retain 10%, then 20% and so on. As the percentage of customers paying in Bitcoin should be low, this should not be difficult to organize. If you only have 1% of Bitcoin revenue, you could directly renounce to use a payment processor and speculate that in the long run your holdings will go up. Of course, a problem may also be taxes on possible profits - not every merchant would like to want to deal with the necessary paperwork.
Nevertheless, a big percentage of merchants accepting Bitcoin via payment processors is of course an important and necessary intermediate step.
What seems to be the biggest problem is the actual number of people who want to pay with BTC at all.
That seems indeed to be a problem. In some communities like Bitcoin Beach the high acceptance is only possible due to Bitcoin supporters having migrated there (either foreigners or from other locations in the country). So in this case you have, as a merchant, a significant incentive to accept Bitcoin even if this means to pay a fee to a payment processor.
And yes, there are the known problems with Bitcoin payments, apart from the already mentioned inconvenience of on-chain payments due to the fees. In bull markets the people tend to hold, they don't want to "lose" their "precious Bitcoins" spending them, forgetting that they could simply re-buy BTC regularly (via DCA for example, or estimating the amount they have spent and rebuying it). While in bear markets, people tend to panic and cash out to fiat. We've still not advanced that much since 2013 it seems
![Sad](https://bitcointalk.org/Smileys/default/sad.gif)
It's however possible that the stricter KYC-related regulations for "cashing out" could drive a new wave of demand for Bitcoin payments, and this could help these "circular" communities too.