Loading and Saving a savegame with World Partition?

So, going through the World Partition stream brought up more questions than it solved.

With Cells constantly being loaded/unloaded, how do we now save the state of the game, especially with multiple layers etc?

It would be quite annoying to have to track all actors and their state whenever a cell is loaded/unloaded, especially given that an actor might move from one cell to another.