mpvl@ is the main author of borgcfg and one of the two designers of BCL (borg config language). I was maintaining borgcfg 2017-2019, and naturally had occasions to chat with him. I was fortunate to learn the existence of CUE a while ago, and was convinced that its theoretical foundation is solid. That foundation is simply not there in most config languages. CUE (along with Kustomize) appears to me to be the 2 major new ideas of addressing the flaws in BCL, and other template/inheritance-based config languages.
I am very eager to see how the community and industry react to CUE.