At first I thought this was just an awful idea, but after hearing what you're using it for I want to use it myself :P
Did you look into the possibility of "adapting" something like d3 to draw on the terminal? Or does it just lack the abstractions necessary to do that cleanly?
Initially I used chart.js to paint the charts but I had to introduce it so many flags (no label Transformation, sensitive spacing etc) that I reverted to do it myself (even though I also have a working version with an altered chart.js).
I am using node-drawville which provides an Html5 canvas Api abstraction over the terminal. D3 uses svg so it is not adequate. However I did saw a port of d3 to canvas which I didn't had time to check.
Did you look into the possibility of "adapting" something like d3 to draw on the terminal? Or does it just lack the abstractions necessary to do that cleanly?