It would be great to have a navigation provider that works off of a repository index. We find that we use Assortments often just because of the assortments navigation provider since it hides empty ecom groups. However, we have some projects that have proprietary products that vary per customer. So it would result in hundreds of assortments.
Instead, if there is an IndexNavigationProvider, it can build the navigation based on an index that we control, and we can have a filtered result in the navigation that could be different for 100 different customers.
There is still a place for assortments but this would give us a choice of method depending on the situation.