I only said html/javascript because they wouldn’t need to do much to add it. Just invoke an instance of the default browser inside the panel and use its rendering and javascript interpreter. This might take very little time or effort. There are a ton of people who can write javascript. I have never heard of Rhino. It may be much much better but I would have to learn it just to make plugins for renoise.
Maybe there is another really easy or good way to build this.
*Edit I should have read the other links first. Rhino is a Javascript implementation.
this idea of internal scripting is fully discussed under:
https://forum.renoise.com/t/idea-for-a-simple-advanced-edit-scripting/18824