Proportion Plot?

I came across this blog post: and thought the proportion plot described there would be interesting to implement.

My first thought is to create a function that generates an array of points forming the curve between the y1 intercept and the y2 intercept, then feed that to go.Scatter(). Before I did all that, I thought I would ask if anyone has done anything like the below (from the link) and if so how they did it.

Thanks All!