As far as I can see Bokeh only supports rectangular bounding box Label types. Are there any plans to support other types of bounding boxes? Matplotlib has a nice selection of other types that may be more visually appealing and offer secondary functionality:
Personally, I would really like to see a round type of bounding box.
Recently Text glyph including support a bounding box with rounded corners (see border_radius attribute). We have submitted a grant proposal to add other bounding shapes to text-like glyphs, especially ellipse, and are waiting to see if it is funded.