Diplexing can't be done quickly as it requires the custom construction of a combiner than takes quite a while to do, and probably even longer in the current pandemic environment.
In the Metro Boston area, tower real estate is at a premium, you would NEVER get a new tower site established as the purchase or lease of the land would be multiples of what the license is worth.
That is one of the reasons WXKS AM 1430 was just given away by Ocean State Trust/ The Evil Empire, and he group that got it has a connection to Salem so a move to Salem's 590 tower a mile away is a no brainer
It was what killed WMEX before Ed Perry bought the license for 100k and found a site to diplex from.
WLYN and WESX are on a tower in the middle of what used to be a junk yard, friends of mine bought the junk yard and spent over 3 million dollars to remediate it, you can bet that there will be a condo project on it at some point as that is what they do, build housing. WESX lost their tower location at Endicott College requiring the move.
When I was with WLYN circa 2006, the VP of Engineering came up and was talking with us about building out a new site, I told him there was no place in the area where we would cover our C.O.L. at night that could be purchased for reasonable money, and 14 years later they are still on that tower in Lynn.
The only time I heard of someone filing for a C.P. to move to a newly constructed site, an application that was pulled back within a month, was WROL trying to move from that old TV tower on the Lynn Marsh Rd just south of the RESCO trash incinerator to a spot in back of Kappy's on RT 1 North a couple of miles away. At least a decade has passed since that filing and withdrawing the application, and they are still on a tower that looks like it is one good King's Tide away from falling into the Rumney Marsh.