Researchers have found evidence that diamonds have formed (and probably are still forming) beneath the surface of the seafloor. In a laboratory setting, these researchers performed a series of high-pressure experiments using marine sediment samples and peridotite rock. As soon as they had enough pressure and temperatures, salts began to form – and with them evidence of diamond inclusions and diamond formation in antiquity in the deep sea.
Granted, we still will not see any more diamond clusters because we know a bit more about their origins. We will still see diamond mining around the world, and the ever-pervasive 1938 De Beers engagement ring campaign continues. They do not seem to hoard diamonds as they used to, but the price of diamonds remains high ̵
Sure, diamonds still have intrinsic value – just like everything else. If I'm willing to pay X $ for a candy bar, this candy bar is (probably) worth at least $ X (at least for the person who made the purchase). But if you have a chocolate planet, this candy bar does not seem to be that rare. *
That and the few reasons we have written about in the last ten years. Like the one about this huge diamond cache, which is probably 100 miles below the Earth's surface. We just have to dig deeper.
Consider also the alien diamonds that hit Earth in meteorites – because other planets in our universe are mostly made of diamonds. Like this earth-sized diamond that you may remember from 2014.
For more information on the above-mentioned salinity inclusions in diamonds, see the research "Melting deep-bed sediments leads to saline inclusions in diamonds". This article was written by Michael W. Förster, Stephen F. Foley, Horst R. Marschall, Olivier Alard and Stephan Buhre. This paper can be found in DOI: 10.1126 / sciadv.aau2620 and is in Vol. 4, no. 5, no. 5 of Science Advances of May 29, 2019.