Maintainer of jsonnet-bundler, kube-prometheus and some monitoring mixins, that are all based on jsonnet, here:

Currently we're mostly keeping a close look at CUE, but not really using it as of right now. However, during the holiday break I've been trying to get into CUE again and there are some things I need to figure out before being able to tell how to incorporate or replace some of our jsonnet projects with CUE, if we really want that.

Some parts of CUE seem like an obvious improvement to what jsonnet currently offers. So 2020 will be exciting in that regard.