Good points, but no matter how done it would increase the force needed for extraction. As the bbl ages/erodes the etcher would be subject to same process, at possibly an increased rate due to gasses swirling/jetting around raised or recessed area. Junk would build up around etcher, thus rendering it unreadable, etc. This idea is technically frought with problems.
As you point out, the freedom implications are even bigger.
Don't get me wrong, it's not that I think it SHOULD be done at all, but by them saying the technology isn't there is utter nonsense. With todays laser applicators we could do this for pennies apiece to the parts, but keeping track of them afterwords would be a nightmare during production. You couldn't see them with the naked eye, knowing they are the right ones with the right serial number would be a pain.