I really like the idea of iteration 7, but I feel like it would work a lot better with some minimum height on the y axis. Letting it peter out to zero loses the "spectrum-ness" of it, and it just looks like various random color blobs. Maybe could have a fixed minimum height, and somehow use saturation to distinguish "truly zero here" from "really low amount here".

Visually the results are very compelling! It also gives an at-a-glance intuition about the image that the bar-style options fail to convey. I am a fan.

Is there source available for this?

Now make it polar and you almost have a vectorscope...