It is a fairly significant limitation of the language today that structural types flat out do not support protocol conformance today, and it is a language change to break that assumption. I wouldn't personally expect much contention from the high-order idea that tuples have these protocol conformances, but adding them as a special case does have interactions with future language directions (allowing structural types to conform to protocols, variadics, and such) that need to be considered, and for some conformances like Codable, there are design decisions to be made about what the behavior should be.