It's a flaw in all current cryptocurrencies that they suffer from an opaque, trust-based exchange infrastructure.

I'd argue that it's inherent in the sense that none of them factored that into their model. As such, I'd argue that the models are inherently flawed because a trustless core is fundamentally compromised if you only have a trustful interface to the rest of the world.

To that end, I agree with your basic point: you need an interface to the outside word that has similar properties to the core model. At least, trustless, transparent, auditable. Probably anonymous as well.