There is going to be such a coin, and it is backed by none other than the UK's Royal Mint!

I think this will be a good stablecoin, as long as the demand does not exceed the limited supply of gold they have in the vault. Otherwise that will skew the coin price away from spot gold prices.

https://www.cryptoinfomag.com/2018/02/01/the-gold-standard-is-back/