Edit: Instead of making another post, I'll add this here. It also feels odd that concerns about xerrors.As possibly panicking at runtime are considered addressed by the addition of a go vet check: https://github.com/golang/go/issues/29934#issuecomment-46252...
I am not opposed to go vet, to be clear, but one of the aspects of the go compiler is that it does not warn, only errors out if compilation can't proceed. But the design of xerrors.As is fine because go vet acts like a compiler warning might? This is an aesthetic complaint more than anything else, but it still doesn't sit right with me.
My apologies, I seem to have confused the two packages. I don't see it in the godoc either. In which case I echo your desire to have an explicit method of formatting and wrapping.
I suppose it won't take long for a component of one of the gometalinter or golang-ci or whatever to develop a "Errorf used without %w in the final position" warning, which will be good enough for me, but it would be better to have something like Wrap officially, IMHO.