I've seen myself in need of some kind of "smart folder" feature.
Pretty much the same (or similar) behavior as Smart Objects, but where a clone folder (slave folder, if you will) will mimic the master folder. Unlike a Smart Object, there's no need to go inside the file, make the changes, save it, go back to the main document and, if more changes are needed, do the same thing again. In certain scenarios this can be a workflow killer. Also, Smart Objects have two issues in my opinion:
1 - Their dimensions are 99% of the time NOT the same as the document (unless we create a workaround, which is almost never the case) so we never really see how the changes are affecting the document itself in real time
2 - Once the Smart Object is created, it's not that simple to rename its name (not the layer's name, but the Smart Objet's name itself, the .psb file). There's a workaround, but it's extra clicks and it kills time.
So having a Smart Folder would allow the user to add/delete/modify elements inside the master folder and all clone folders would mimic it. I believe Adobe XD has a similar feature. I haven't used it in a long time, but I guess it does.
This is good to not having to leave the main document and being able to see the changes in real time.