My concern with this is that when setting up a detail, it is handy to flop back and forth between model and layout space, panning, pulling detail borders, getting the bits in the detail you need, keeping scale constant. Adding the details as viewports when unlocked behavior seems to me like introducing another way off messing up the detail inadvertently.
Part of my hesitancy also stems from the fact that UndoView is so unreliable in details. It will get you back to the step after you messed up the detail, but never, and I do mean never, in my experience to before you messed it up. Restoring a detail you messed up because you assumed it was locked and wasn’t can be a real pain (when dims, notes, section lines etc are in layout space and you have to line everything back up again). If UndoView can’t work in an active detail, I would imagine Undo / UndoView would also not work on an inactive unlocked detail who’s border had been modified. Perhaps if UndoView was more reliable and robust in details and a more obvious locked indicator for both active and inactive details would allay my fears, but as it is now keeping details from getting messed up would be a priority for me.
I’m all down for detail scaling though.