What is the axis of rotation in a high alpha roll? When doing an aileron roll at a high alpha (say 25 degs), which axis will the aircraft rotate about?

Is it the incoming air-stream vector or is it more the body X axis? And does the pitch inertial coupling factor into this or is that an unrelated phenomenon?

I am thinking in terms of high agility aircraft like for example the F-16.
That depends on the control system of the aircraft, in case of fighter jets with fly by wire technology and modern fly by wire airliners the yaw control law usually tries to rotate around the velocity vector, which in calm air is the same as the incoming air-stream vector. (according to my university lectures)

The difference in the target yaw rate (r) is just the body roll rate around the x-axis (p) times the tangent of the angle of attack (with the sign flipped, depending on which coordinate system you use).