Also, brilliant.org and exosphere.app, both with large and active Elm code bases. I worked for brilliant for a time and now work for exosphere.

Also, my own project, https://scripta.io. About 45kloc of code split between the app (lamdera/elm) and the MicroLaTex-to-HTML compiler (elm).

Have been working with Elm for five years and have been happy with both the experience and the results. E.g. radical refactors of core data structures are simply no big deal.