you will notice that the F-59PHIs have been kept close to SEA. It may be due to very restricted parts availability. If that is the case once the Chargers are approved for regular Cascades service then if they stay in Amtrak service they will need to be assigned to a base that will acquire all the parts.
That limitation would seem to limit them to Oakland, LAX or CHI. On further thought maybe New Haven as well ? That would cover the Springfield - Vermonter trains and free up the P-42s to cover the overextended LD fleets ? OAK, LAX, or CHI might be just temporary as the Chargers all start covering the SD trips out of those bases.