A few years ago I was on a project needing a solution for developer-facing graphical views that are remotely accessible. It needed to be simple for developers-- like being able to code the visualizations along side the code being inspected-- and have zero overhead when not observed.
I ended up with a framework that is just building up canvas JavaScript code and shipping it to a web client over websocket for eval. It uses a graphics API based on Processing, so the developer needs no knowledge of HTML canvas / JavaScript. The current implementation is for Python, but other languages could be added using the same protocol.
I wasn’t aware of Hotwire until someone brought it up during a PyCon talk covering my framework. Hotwire makes sense to me! 