According to the acousticians, undercutting, chamfering or fraizing (as you like it) can have a significant effect on response--much, much more than wall material. Getting rid of sharp edges in the bore reduces turbulence and internal reflections in the air column, and it is highly recommended when- and wherever it can be done by Nederveen. As regards headjoints, I have some personal experience. First, I had the embouchure of my bass flute redone a couple of decades ago by a man in Modena, Italy famous for redoing head joints, and the difference was *amazing*. Second, I have a Cooper-style headjoint with undercut chimney sides, and the difference between it and a classic Boston-cut headjoint is huge. Of course there may be other factors at play (such as the curve of the headjoint tube), but the ease with which it blows is, I think, indicative of a much better coupling between the air jet and the air column.
Basically in thin-walled metal instruments you can't actually round the edges of the tone holes, you have to curve the bottom of the tone hole or embouchure hole chimney so that it does not meet the body tube at a right angle. This is not easy, and my Cooper-style head joint was significantly more expensive than a standard Powell head. Doing this on the tone holes would add a lot of cost to a handmade flute.
But extruded tone holes? It seems to me that it would be a simple matter to draw the tone holes in such a way that would mimic chamfering. I wonder if anyone has tried this...
Toby