So I've successfully done all the updates mentioned, and attempted my first run with this process. It did NOT work.
36,191 images in my LR at the point of 'Edit in Photoshop' - PS launches, image appears, I make adjustements, duplicate a layer or two, close the file (and obviously agree to save the changes), image closes, and when I go back to LR (and wait a few mins to be sure), nothing has updated with the modified image.
I still have 36,191 images in my library.
So, these updates have not made any difference to me.