The problem with spacing out the bottom of the steer tube would really be the bearing race. You'd have to find some way to mount it to the top of the spacers. You could get a framebuilder to extend the headtube.

And I think the brake cable issue would be complicated by the little clearence between the fork and the tire. It needs a good amount of space to make a smooth curve.

I think these issues were solved by the BMW Gangster, and that bike is hideous. Luckily a few framebuilders are making cutouts for the front wheel so people can do barspins with normal geometry.