Shouldn’t be. Especially if there won’t sublevels in the proper tile-streaming system. Every actor instance will be stored as a separate asset on disk. Basically, our sublevels would be converted to as many files as actor instances.*
At least that how they present the new system in their presentation a long time ago. And how it works in open-world engines I worked with 
- Unless… Epic would use something like “layers” to group a small number of actors together. It would be useful for scripting, i.e. “load destroyed version of the village in response to the player decision in the story”.