Grafana have been working on a replacement for grafonnet but unfortunately haven’t shared much detail. It sounds like they completely rewrote the dashboard spec using CUE, but there will be converters available at release.

In some of the discussions where the community is trying to figure out how to future-proof current dashboard definitions, Grafana Labs has also recommended this Python tool (unofficially I suppose) by Weaveworks, called grafanalib: https://github.com/weaveworks/grafanalib