Yes; the paper mentions CodeMoo.com, which the University of Illinois created independently of us to teach basic programming skills to kids [0]. The file system component is readily used by the Internet Archive for their MS-DOS collection [1]. A number of other instructors approached me regarding using Doppio for in-browser IDEs, but Doppio is somewhat cumbersome to integrate into webpages, and never had the time to dramatically improve its documentation and ease-of-use. I believe that is a more fundamental barrier to using Doppio than its performance, especially since you can run Doppio in a WebWorker to avoid some of the responsiveness issues.
Also, note that Doppio is an interpreter, so there is significant interpreter overhead. Using a JIT compilation approach would improve performance, and a contributor is currently working on a basic implementation. I honestly believe that it could become significantly faster with additional work, but as a single person with other projects, I lack the resources to do this work myself.
Have you encountered any practical use cases?