What do you think about GGSQL, or is that not entirely aligned with what you want? They also produce vega-lite JSON as output.
I've been mulling extending dbt Charts to support ggplot, and will likely reach out to the team about this in the next few weeks.
The difference is that Vega-Lite, ggsql, ggplot2 are designed to create a single chart. Yes, you can use facet_wrap() to great a series of charts based on a particular variable, but arguably that's still one chart!
What's missing that is table stakes for a BI dashboard: KPIs, text boxes, dropdowns, data sources, governance, and how the charts are arranged on the page and in relation to one another.
In the next few months we hope to ship a JSON schema that represents a dashboard in the same way that a VegaLite does for a single chart.
Does that make sense?
I guess at the moment GGSQL itself wants to be directly connected to the source database, whereas you've got a split between queries and the charts which display the results.
It would be really cool to have SQL "all the way down" to the chart definitions as well :)