https://observablehq.com/plot/marks/raster https://observablehq.com/plot/marks/contour https://observablehq.com/plot/marks/cell
We generally recommend stacked bar charts over pie and donut charts, so we haven’t prioritized those. But you can already implement them using custom marks, and there’s even a hacky way of doing them using Plot’s map projection system.
https://observablehq.com/@observablehq/pie-to-donut-chart
I don’t understand your comment about the “D3 example.” If you’re looking for Plot examples, you can find them linked from the Plot documentation and the gallery:
https://observablehq.com/@observablehq/plot-gallery
Plot is designed to be extended with JavaScript (rather than a non-JavaScript DSL such as Vega-Lite), such as for custom marks and data transforms. So you might occasionally see other libraries being used together with Plot.