I feel like this is a great practical example showcasing the value of static types and designing your data model up front. If you know the structure of the object, you can put in placeholders while the real thing loads in. Then you get to choose how it loads in. Ideally you can stream the patches via serialized actions. This is basically Redux/Elm in a nutshell where the action objects can come from events sent via SSE/websockets/polling/etc.

Reducing a change log is about as stateless, functional, and elegant as it gets. I love these sorts of designs but reality seems to complicate them in unexpected ways unfortunately. Still worth striving for though!