The Elm Architecture is not that super novel. Actually it came from game development from the Components way of thinking. Take a look at this book. It's a classic for gamedev:
- https://gameprogrammingpatterns.com/
Elm seems stagnant because Evan is not so transparent and prefer work in a private branch and to release work in batches instead of having a release every 6 months, this makes people think it is dead. Elm is still being used in production by dozens of companies with huge codebases (100k~400kloc), and the community is very active, there are amazing projects like elm-pages, elm-review, elm-ui (from mdgriffith), elm-spa, elm-charts, lamdera and others.
Most of the activity happens in the (public) Elm Slack community, so it's not indexed in search engines and hard to find in StackOverflow, but it's a really effective place to get advice and help with a problem in a more personal way