Very interesting...but. If the anti-phase signal is successful, and this is a big if, the target frequency range will be eliminated from the sufferer's hearing. To a pilot, this is not altogether a serious problem career-wise, because their main concern is reliable use of the radio, and in most tinnitus cases this will be ok.
However, there are many folk, like me, who value the upper tones while away from their noisy flying machines. I spent thousands of hours learning to play classical piano, and to my dismay found that the higher end frequencies were beginning to sound very wooden. On a happier note, (ouch) this was stable over the next 20 years, and I just had to learn to put up with it.
Strangely, I often make a comment about a soprano or mezzo soprano which is then substantiated by an accredited critic. I have no idea how I am able to make subjective judgements about sounds that the CAA say I should not be able to hear. The holographic modeling of hearing is fascinating, and I gather, at the limits of understanding.
Just a mention. One of the leaders in anti-phase sound processing was the electronics dept. at Essex Uni. Near Colchester. I went to see them c 1979 to see if there was a possibility of quieting the horrible noise in the turbo-prop that I was training a succession of new pilots on. At that stage they held out little hope of it working. After 800 hours of circuit and line, I was introduced to the whistle that I can here at this moment.