One thing I always dislike about Elm and most of its offshoots is the lack of good composability of widgets. In most other architectures, most widgets are registered with their parent component in one single location, and are otherwise fully self-contained.

In Elm-likes you usually need to explicitly need to connect all child components in the model _and_ view _and_ update in a way that ultimately connects all leaf components to the root component. I know that there many Elm proponents that see that as a positive (as that makes execution more transparent). However in practice that usually ends up with either overly shared Message types where logic isn't contained to the widget it belongs to, or a boatload of boilerplate just to do .map operations between a child-Message-type and it's wrapping parent-Message-type.

I think this boilerplate can be solved by some degree with good framework support (and some try), but most Elm-likes don't and it makes scaling projects in them a pain.