Thanks for your reply @jdb! As you can see below together.js is now being maintained by the JSFiddle team. Using the information in the issue you sent I was able to get sharing somewhat working. When I move the cursor around on my laptop, I do see that on my desktop which is very cool. However, the clicks on one computer (e.g., on a tab or selecting variables) are not reflected on the other computer.
I wonder if this is because shiny creates single page apps, the way my app is organized, or some other reason. Have you been able to get it to work with shiny apps in the past?
https://vnijs.shinyapps.io/radiant-data
FYI I did see a few uncaught errors at some point ...