I would assume that the creation of an additional district or two would give Trump an opportunity to appoint more judges and it would diminish the power of the 9th..
Similiarly, Robarts in Seattle might think about retiring if he was forced to work a Phoenix court. Less mess, less squealing than impeachment proceedings would surely generate.
The extra judges , as you say, will garner support from local kingmaker senators to get the ball rolling with dismantling of the existing 9th Circus Court of Appeals.