Sciolistes, you will cross the IAF, it's just that instead of wasting a lap in the racetrack which is completely unnecessary as you are already established on course and altitude, you continue straight in.
There is absolutely no valid reason to complete a racetrack or course reversal procedure if you are already established on the desired and depicted track and altitude to continue an approach. This is not even a discussion, the question is whether it is legal to do so or not as the racetrack is depicted as part of the approach procedure on the approach plate.
aterpster:
I understand your example, but it does not necessarily have to be vectoring. Just to give you an example let's say you are on an airway somewhere or whatever (doesn't really matter) and ATC says "descend to X feet (altitude for final approach segment) proceed direct to X (name of IAF), cleared X approach" and as a complete coincidence when you turn direct you see you are established on the exact inbound course. You maintain this inbound course as you navigate towards the IAF which also is the start of a course reversal procedure to establish you on the course you are already on.
Assuming these conditions, would you complete a lap in the racetrack or not?