As @Chris_Lattner3 said anonymous syntax is it’s own design space. For me the full potential of that would be to have a wide reaching shorthand that covers wide variety of types: anonymous structs, anonymous protocols (existentials?), anonymous generics, anonymous typealiases, anonymous associated types and so on (don’t know which ones make sense).
To design that space well, would mean that it’s applied to lot of those types from the start, not just as a byproduct of opaque type feature.
Likewise, ideally I’d like to see opaque types designed within the existing Swift syntax, ensuring it fits well to the language as is, and then later augment it with the general implementation of anonymous types.