I took a look at the description of your issue and I think at this point we might not have a strong solution for you. One reason streaming works so well when playing games is because we can roughly judge what you as a player can see based on what you are near in a level. When creating content in studio a user can be anywhere in a map in a matter of seconds and if we were to enable streaming in the editor we would have to be able to predict what the user wanted to work with even if they were far away from their work. This may be something we consider in the future, but in the short term I would look at doing the following.
I would try to load up the map on another computer. By breaking the map down into small pieces and saving them separately, you may be able to edit them from your macbook once again. It sounds like it's run out of memory. If you would like to edit it at its current scale, you may have to reduce its complexity. You can also try shutting down all background applications before editing the map. Really anything you can do to reduce how much memory you are using, the more likely you'll be able to edit your map.
Thank you for taking the time to explain your issue, this is an interesting idea we may consider for the future, but in the short term this solution may not be integrated.
Roblox Developer Relations