I think that the question is, why wouldn't you? There are already a lot of work and testing done on projects that depend on 1.12 features, but using beta and rc releases. Final 1.12 version would just confirm that everything works, but without docker image, testing on staging infrastructure is delayed even the final version is out.

This is why I have https://NewReleases.io configured to track both Go GitHub releases as well as golang image tags on Docker Hub.