4. I agree that the current duchy system makes this kind of thing too easy. It was not possible under the old system.
What exactly prevented this in the old system? I can't access the political map from the wiki right now, but FR was a two-city realm (Via and Golden Farrow), right? Then all the rurals could swear allegiance to the non-capital city in the old system too.
I would be a big fan of a system which would remove the possibility that clicking a button in game results in a forbidden result.