Starnuts are good in their own place. But this doesn't seem to be the right place.
Even if you shove a quill style wedge up the steerer tube it's going to be better than just a couple of starnuts as it has 3 or 4 inches of metal before the wedge. The wedge will simply be holding the mechanism up in the tube.
People have mentioned flex coming from the material thickness. These are all from pulling forces. If you put the brake on the rear of the forks the surely it will have the crown of the forks to push against. Ok, it doesn't look pretty but it might work better.
Starnuts are good in their own place. But this doesn't seem to be the right place.
Even if you shove a quill style wedge up the steerer tube it's going to be better than just a couple of starnuts as it has 3 or 4 inches of metal before the wedge. The wedge will simply be holding the mechanism up in the tube.
People have mentioned flex coming from the material thickness. These are all from pulling forces. If you put the brake on the rear of the forks the surely it will have the crown of the forks to push against. Ok, it doesn't look pretty but it might work better.