A solution to NOT drill your track forks and have a normal front brake nonetheless

Difference being that star nuts weren't designed to have much load on them. They certainly weren't designed to resist braking force.
A wedge will be more able to take the tightening that this idea requires.

IMO.

Of course.
(theoretically) Attach some handlebars to the SFN bolt and apply pressure one way or the other, the SFN will move immediately and likely bend over in the steerer.

apply the same pressure on a quill stem...

of course it will be ok, because it's made to take those forces.

A good solution would be an expander bolt or wedge system that bolts from the higher part inside the steerer (just under your stem) with a long bolt going down to a nut/bung arrangement which holds the brake bracket securely into the tube at the fork crown.

Thing is, the whole situation is a faff, a solution to a problem which doesn't really exist. There are clamp on brakes for keirin frames and proper forks designed for use with brakes if that's what you want to use.