I switched to use a document fragment instead of a D3 G selection. Is it necessary to use multiple plots within each subplot here, or could we do this as a single plot per subplot and instead add marks as necessary?

Well, it seems to work with a single plot. 😅

Thank you for the changes!

Would be very neat to also make a brush selection to enable the reader to explore subregions of the data space.

yes, it's the logical next step :) stay tuned!