That was the first feature I was looking for in the 4.1 changelog , it would make the design workflow, especially with more than one part, so much easier.
C'mon Slic3er, Repetierhost and Cura have it too!
Or even a symbol next to the part name noting a part file has change giving the option to update the part. Maybe not automatically but at least let you know there is a change to the original part. a simple record part location and date last modified?
I came here just to suggest this feature. Many models I reload 5-10 times tweaking the model to improve printing.
I've used a text compare program that pops up a notification "File has updated on disk, reload?" if the file changes. This could be disabled in settings, but if the file ever updates, there's a reason.