I still think there will be an out going special addition Boss utilizing the 7.3 Godzilla before EV MY28 Mustang. Because that's a lot of unnecessary engineering specific to the S550-650 chassis to not use it. One can only hope.
I think there is a strong possibility at this point. Ford put it in the bulge mustang to test out a manual controls pack, and possibly to test a future engine combo in the mustang chassis. They also developed a car specific intake manifold for a reason. They could just destroke the 7.3 about an 1/8" and get a modern 429. It could be the last hurrah for a purely ICE powered V8 mustang.