If this is useful, I wonder if an ordered set is useful.
An ordered set is a unique list. It's useful. However it's not present in Python, dicts and sets have separate implementations and sets were not moved over to the ordered implementation (because the ordering was initially a side-effect of a change in implementation which was not considered useful or advantageous for sets).
With ordered dicts you can use the trie to compute your autocomplete very quickly with no additional data structures. There are lots of other trie operations which are more efficient with ordered dicts too. I’m sure someone can come up with less complicated examples but this was the first one I thought of
I guess a better use case is if you needed some sort of priority/FIFO logic along with indexing. Hard to think of something that doesn’t feel contrived, but I guess imagine having a queue where determining membership or updating fields of an element based on ID can be done in O(1) for any element?