There was some discussion back in 2016 about the empty initializer requirement of RangeReplaceableCollection. I'm not sure how feasible it is at this point considering source compatibility, but I've always hoped that this would eventually be revisited and the requirement could be removed. I have some custom collection types that have additional stored properties with no reasonable default value. It's useful and makes sense for them to conform to RangeReplaceableCollection and get all of its built-in functionality, but the empty initializer requirement makes that problematic because of the non-defaultable properties. I'm currently hacking around it by trapping in the empty initializer, but that's obviously not ideal.
I don't want to hijack this thread to discuss that change, but I wonder if the functionality of this proposal could instead be split into a separate protocol so that we don't add more APIs that rely on the empty initializer of RangeReplaceableCollection.