The ideals of a moneyless society by virtue of just being in the freaking future in TOS and then later because of replicators in TNG and beyond had to be adapted for the multicultural bazaar on Deep Space Nine by introducing Gold Pressed Latinum. Something that replicators couldn't reproduce. I think that is an interesting thought experiment. The only currencies on a federation ship are friendship and duty, but once you add in a mix of cultures and the complexities that develop because of their clashing goals and desires, you need a scarce item to keep accounts. We've done it over and over throughout our human society. My favorite is the Rai Stones[1] from the island of Yap, where they can't even be moved for the most part. The transfer of ownership is purely a social construct.
Diamonds are interesting and I think unparalleled in their arc as a store of value because of how technology is eroding and changing that. Not just the ability to produce them, but information technology swaying trends relating to their status and ethical usage. You can't tell a blood diamond from anything else once it's mixed with others. Some people see diamond jewelry to be akin to wearing fur. Some other people still find the suffering that came from their extraction to be part of the value. Not going to debate the morality of that issue, but I've heard it expressed more than once. Suffering will always be more bespoke even if the item can be identically reproduced. Some might prefer to soften "suffering" to "effort", but I'm unaware of an ethical diamond mining operation. Like lab grown meat, a strong case can me made that once we can make the thing in the lab at scale it is absolutely unethical to extract it from the earth at scale for vanity. No excuses.
In some ways suffering as a store of value is sort of like the social construct of a rai that floats with the idea of the item. Maybe we can build a crypto supply chain technology to verify chain of custody on natural diamonds so you can correctly track the bodies on it and their value in relation to your net worth. I'm only sort of being glib here, making it an accurate record would undoubtedly make them less romantic prizes.
Surely the tools and equipment to create synthetic diamonds will continue to drop in it's price to own and operate. It will be interesting to see how De Beers handles the first online custom gem shop where you can set your specs via your browser and have your gem grown to order, cut, and drop shipped for the price of a latte.