I know this is late, but I'm changing my response to -1. I tried for fun to integrate antitypical/Result into PromiseKit and because the Result type requires a concrete Error type to be declared it made it impossible to use this form of Result.
I believe this was acknowledged in the thread with a potential solution, but it is not acknowledged in the proposal.
I don't see the point in adding a Result type to the stdlib if projects out there that need it cannot use it as proposed.
Further using antitypical’s Result was continuously tedious due to the need to always declare which Error was involved. Sometimes it seemed impossible to use it since a particular area I needed may return multiple types of error.
I think adding as proposed wouldn't help nearly as many people or projects as people have implied here.