the problem is that for each inner ear anatomy the subject hears the distortion as "normal"---if they hear a live performance the sound is put through the ear anatomy and processed by their ear anatomy just like every other sound they hear. if you corrected this to an ideal ear anatomy the person would hear a sound that is totally abnormal for their brain to receive and would not be pleasant or realistic. This would not be true for bone conduction phones which would have to be balanced to reproduce the distortion of each persons ear canal in order not to be sensed as alien.The personal variance of ear canal anatomy above 8kHz is so wide, that no amount of generic single dummy-head measurement can ever approximate the what it really sounds to YOUR ears.
Still, the development of less variance in headphone measurements is important and very welcome.
Now, if we could actually simulate differences in "normal" ear anatomy and have a range of measurements that show how differently a pair of headphones can sound on different heads/ears, that would be the next step.