Where is the inclinometer "ball" in a knife edged turn?
As it was pointed out in the other thread, the ball just rolls around inside a curved glass tube.  It doesn't know what the angle of bank is, or anything other than what direction gravity, and/or centrifugal force is moving it.  Therefore:

At 90 deg AOB in coordinated flight at positive G, the ball would be centered.  The aircraft in this case would be in a descending spiral.

At 90 deg AOB in a "knife edge" straight pass where altitude is maintained with rudder, gravity will pull the ball towards the earth.  Same thing if you were able to make a knife edge turn holding altitude with rudder.