Precious metals are becoming sort of an oxymoron in my opinion. What's so precious about gold? It serves a purpose in some electronics, but so does copper and other cheaper metals. You say it has scarcity? Only temporarily. We could extract more from earth but it isn't even that profitable anymore now that Cryptos are on the scene. If you want to collect something physical that is considered "precious" with intrinsic value, look into rare minerals.

Once cryptos become a little more mainstream, I'm thinking UNO could easily integrate with the precious mineral community.
I realize this comes off as a bit crazy, but when you consider the innovation around 3d printers, we're looking at a world where just about anything can be produced with ease, except for a few things such as minerals and Cryptos.