I don't have a good answer for that at any time before fiat volatility increases massively. It's something I've spent a lot of time thinking about

I price in fiat still as I am in an area where there is very little knowledge or use. My underlying preference for bitcoin lies less in angling for personal future wealth and more in creating a fair and stable market unlike our current chaos. Decisions about pricing therefore are based on incentivising Bitcoin use, building local knowledge and trust. But, as you say that will change. If we continue using it as a store of value and not for exchange, so much is lost. Its function as a better tool of exchange is lost and it becomes about the political manoeuvres of the whales and not the bottom up, intentional shift it offers us.

can you imagine customers being displeased that your prices keep falling? this is what @SweetSats does and it's glorious

A merchant could price the product at the fiat price of the product. Example, a bag of potatoes is priced at $5.99 in fiat at the grocery store, so simply convert the satoshi price to its equivalent. Only adjust the satoshi price when the grocer adjusts the fiat price such as before or after a sale discount that week. No need for constant price fluctuations by the minute.

Pricing in fiat and converting to satoshis is a sufficient transitional step until we reach the Bitcoin Standard. It avoids the constant minute-by-minute volatility of Bitcoin's fiat price.