I finally decided to update from 3.6 to 4.6.2 as there's been sufficient advances in the software it seemed hopefully worth it (and the sidebar plugin is a thing, which fixes my dislike of the post 4.0 UI).
For the most part it seems workable, with the exception that the Build Plate Selector has seemingly been replaced with the Object List, and sending an object to Build Plate 2+ without having a model loaded on Plate 1 removes the object from the Object List, making the object on plate 2 inaccessible.
I had been using the multi build plate functionality in 3.6 for multi object prints by sending items from Fusion360 to a Cura instance and moving them to the second build plate, as fusion 360 clears the build plate when it sends a new model (rather frustrating in that aspect - didn't happen on Mac OSX but does in Windows 10 for whatever reason).
For reference, how it used to work in 3.6:
Send Model "A" from Fusion, it arrives on the Default Build Plate
Select Model A and right click -> "New build plate"
Model A is moved to Build Plate 2, and I can switch between plate 1 (empty) and plate 2 easily using the selector.
How it seems to work now in 4.6:
Send Model "A" from Fusion, it arrives on the Default Build Plate and is added to the Object List located where the build plate selector used to be
Select Model A and right click -> "New build plate"
Model A is moved to Build Plate 2 and is removed from the object list (interface now appears identical to when no model is loaded on fresh boot).
Send Model "B" from Fusion, it arrives on the Default Build Plate and is added to the Object List.
Model "A" reappears in the object list once model "B" is Added to plate 1, and by selecting model "A" vs. "B" I can swap between build plates.
If Model "B" is sent to plate 2, both models become inaccessible until another model is added to plate 1
I've read all of the patchnotes since 3.6 and have seen no reference to removing or changing multiple build plate functionality, and tried various key combinations, incantations, holy water, etc. to swap build plates with no results.
Anything I'm missing or is this a feature that's been sent to the shadow realm?