> Struct variant fields are public, limiting how you evolve the fields and types

But the whole point of thiserror style errors is to make the errors part of your public API. This is no different to having a normal struct (not error related) as part of your public API is it?

> Struct variants need non_exhaustive

Can't you just add that tag? I dunno, I've never actually used thiserror.

Your third point makes sense though.