MoI has an Incremental Save shortcut, but this doesnt do the "thumbnail" thing yet. Also remember that "Import and Export" do "Just the selected parts". So you can Select a single object you would like to refer to sand save it to a specific name in your construction folder, then if need for any scene, import the part in. You could build massive scenes and only keep one object loaded at any time. The new "Part import tool" is very powerful also.