I think the best question is whether or not the modifications needed to turn the Qatar 747 into a VC-25B can be completed significantly before Boeing can deliver the VC-25Bs already on order. If not, then there's no reason to sink modification costs into the Qatar 747. No sense in spending the money to modify a third AF1 if it can't be completed well before the others are ready.
Of course, there would need to be a better commitment on Boeing's part on when their delivery will occur.
Right now, the most current delivery date given by the Air Force is 2027.
Boeing's CEO said in 2022 that he expects the company to realize a $660M loss on the VC-25B program after Trump renegotiated the contract. Sounds like a good excuse for dragging their feet on delivery while hoping the next administration eases their loses.
There are two VC-25As used as AF1.
They are both modified 747-200Bs.
The tail numbers are 28000 and 29000.
SAM stands for Special Air Mission. When not carrying the President, the call signs are usually SAM 28000 and SAM 29000.
-- Clinton and Bush used the tail numbers for their call signs when not designated AF1, but Obama used the call sign SAM 44 (44th president).
https://en.wikipedia.org/wiki/Special_Air_Mission#cite_note-4Both VC-25As were manufactured in 1987 and placed into service in 1990.
Both VC-25As were scheduled for replacement in 2017.
The replacement modified 747s will carry the airframe designation VC-25B.
The VC-25B is a modified 747-8, the largest variant of the 747 family. It's a larger variant of the 747-400.
The Qatar gift is a 747-8, the same variant as the two being delivered whenever Boeing gets them completed.