Why not allow call-by-name parameters to functions? That would enable library authors to build whatever error handling conveniences they wanted. This feature dates all the way back to ALGOL-60.
> That would enable library authors to build whatever error handling conveniences they wanted
What I want from a language - especially if it's, like Go, aimed at really big project - is for it to be opinionated and narrowed in options. That's Bill Kennedy's point as well, they're adding a language level feature so now there's one more way to do a very common thing. And when there's multiple ways to do something, they will all get used.
"But what about conventions and code reviews?", you might ask; that's cognitive overload that, if there was only one way, would never be a thing. I mean another feature of Go is that it enforces a certain standard (with tooling and formatters), so that as a development team you should never have to waste time and energy on discussing or arguing about formatting.
I'm not against changing how errors are handled now, as long as they're standardized and the One Way to do things.