I figured out how create a diverging asymmetric colorbar in bokeh and use it in a bokeh chart. Was so happy about that I wrote a blog post about it!
And @BokehPlots has tweeted about it!
I am wondering if this is something you would like to put in the bokeh library. This is somewhere I could contribute to bokeh with a little guidance. First though, is it needed? I have used diverging asymmetric colorbars just a handful times in last few years as a data scientist that creates many visualizations. Too many high level functions can really clutter up the interface!