Here’s an example using D3 to add interactive tooltips to Plot:

https://observablehq.com/@mkfreeman/plot-tooltip

Here’s one that lets you click on a region in a line chart to select it:

https://observablehq.com/@skybrian/select-from-predefined-re...

Here’s using rough.js to stylize a plot:

https://observablehq.com/@fil/rough-plot

Nice! Thank you!

The tooltip example in particular strikes me as a convincing demonstration that there's a fairly coherent vertical stack of tools in D3->Plot around which a useful and flexible ecosystem of plugins and extensions can be built, all in SVG too (of course!)

Also, tangentially ... I just went on to https://bl.ocks.org/mbostock for old time's sake, knowing full well that Observable is your new home and got a Heroku error. Presuming it's because the bl.ocks are no longer maintained, I figured I'd let you know.