>
>
> EWG has rejected proposals like
> https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4172.htm
> before due to the (lack of) opt-in question.
> I don't see how anything has changed in that regard.
>

I'm aware of the previously rejected proposals, and have read the minutes
on those. I don't think that the past proposals failed solely due to the
opt-in question. It was a combination of factors, including not having a
working implementation and not dealing with the design questions
thoroughly enough.

Historically, we also didn't have designated initializers (which don't
require the struct to opt in explicitly), and we didn't have parameter name
reflection (which faces the exact same issue of possible inconsistencies
between declarations). The rest of the language has changed quite
significantly since 2014. IIRC at least 50% of the backlash to N4172 was
due to the parameter name inconsistency problem, and that's now addressed
(though not really solved) elsewhere.