The nested collections are great, but over time they have the potential to grow to an un-manageable number of items.
I think there is a need to be able to filter the items that are displayed in the collection. An obvious example would be to be able to display only the incomplete tasks in a project, or incomplete and recently complete. But I’m sure there are other types of filters that could be useful.
It may even be useful to be able to have multiple views of the same collection in the parent entity.