People say 'stable coins' as if it's a simple matter to create them. There have already been several cryptocurrencies that were meant to be locked in value to a real-world currency or commodity. They all fail in the end, and any system relying on them will collapse when the values diverge.

You cannot perfectly link a real world item to a digital asset without losing the 'trust-free' nature of cryptocoins. You always end up having to trust someone. And once you do that, you've lost all of the advantages of the digital asset.