Personally, I'd like to see the 787 made into a tanker. The airframe has size, range and speed, so should be able to service any aircraft in the inventory. I wouldn't trust Airbus to make a paper airplane in a math class, let alone a replacement for the good old -135! From KB-29 to KB-50, to KC-97 and KC-135, Boeing has built the best aerial refueling aircraft in the world.....why should we go with some French POS?
I guess which model they pick for the Tanker depends on when they air force wants it. Right now Boeing can produce the Kc767a, and has shipped the first two to Italy to be completed (part of the deal). They're not getting any new civilian orders for the 767 so they can start pumping that version out at a dedicated factory.
The backorder for the 787 is already three years. I'm not sure how many backorders they have for the 777. The 757 line is closed. The 747 line is open with few orders left.
But that would interfere with thre production of commercial 787's. That might cause customers to go to Airbus to order an A350. The 767 tanker has already been designed and tested, and it is produced on an already existing line from the 787.
A non-USA tanker should be off the table, even if it is "assembled" in the USA. Huge (all) DoD contracts should be awarded to those who pay the taxes in the first place.