Your previous post fell on an unfortunate date 
My next way to solve custom chart plotting would be either:
-
an integration of Coda <-> ObservableHQ, or
-
a full HighCharts library pack with all the customization it supports
No time to tend to this now but I keep the latter idea in the back of my mind.
Take a look at the Itsy pack. It basically allows hosting custom HTML in Coda. And unlike my SVG hacks, those HTML widgets are interactive because they are served through an embed, not an image tag.