I think “deeply nesting components” means dropping a stateful component (view+behaviour+state) anywhere in your app without anything else changing. That’s not possible in Elm since the only place to store state is the central state storage. Which makes perfect sense, but often freaks people out, since it’s an uncommon design constraint.
With only one store, how do you keep your state reasonably organized when you get up to hundreds of pieces of data to manage?
And what do you do about generic reusuable components that need state? Say a typeahead search that needs to track the input string and the list of results from the server?
If you really really really can’t live without a statefull component, you can always build a custom element (which can be a wrapper around an elm app). But reusable views with fairly complex state are used; they require a little bit of wiring up, but it means you know exactly where to look when there’s a big/problem.
You can think of each root-level branch of the state tree as its own "model". In redux (I haven't used elm much) I implement generic components by finding a property that can be used to derive a unique key and creating an entry for each component in the reducer.
