An AF detect is not going to help doing tilt focus much, you are trying to set the angle of the plane of focus a total different prospect to a normal focus operation on a few AF points.
Presumably live view would help a lot with this, anyone tried that?
I've just done a test to check (24 TSE on 5D).
The "manual-AF" (is it to be called AF-assisted manual focus ?) works fine with shift (up to half way, but not more) or tilt (full range). It may work with shift and tilt but not always. When AF stops working on a given point, I still can focus on a brighter point. I got similar results with the lens rotated horizontal or vertical.
The range of workable AF v/s shift and tilt seemed to be due to AF limitations itself, rather than intrinsic optical properties of the tilted or shifted lens.
Of course I can only focus on a point where an AF colimator is (mostly at the center), which limits the help I can get from it. Was it what you wanted to point out?