I was with you until your comments regarding "snake oil." If more engineers took cables and amplifiers more seriously, perhaps we'd have better recordings to listen. It's the height of absurdity in this day and age to say that cable talk should be regarded as "snake oil," and despite the fact that follow your reasoning and can even accept your comments up to that point, you lost me there. Either changing the cable or adding a 2 meter extension onto a $200 or $2000 pair of headphones is going noticeably alter the headphones characteristics, both in terms of balance of frequency response, forward or backwardness of either solo performances or accompaniment. Everything influences the sound, and admittedly, it's hard to know what is doing what, but real world experimentation with cables and amplifiers, mixing boards, microphones, AND headphones all alter the signal in audible ways, just as much as room treatment. It's unfortunate, because it adds to the difficulty of coming to any solid conclusions, but that's the world we live in, and we just have make the effort to learn to evaluate what we recording by listening to the final results and a wide range of systems outside the studio and then work backwards comparing all those different experiences to what he hear in the studio. Some will suggest using measurements but I'd say that route is even more flawed. True, people do hear differently but the human ear, in the end, if it is still working properly seems to trump measurements any day of the week.
I loved your practical suggestions also, don't get me wrong. On the other hand, I think the notion of buying headphones for an engineer is doomed to failure unless the engineer gets to pick them out. A better scenario would be to give the budding engineer a gift card with a pre-paid credit card, and tell them to see if he borrow a few different cans, and discover which one he/she is most appropriate. There are number of intangibles, aside from mating the headphones to the recording equipment, not the least of which is comfort. What I can tolerate for several hours might not "sit right on someone else. And buying based on what the industry uses may sound like a good idea but then again, it does depend in part, what the equipment is, and what type of music is being recorded and mixed, whether it's live recording of rock, folk, jazz, or classical. I'd give him the credit card and let him/her duke it out by experimentation. Otherwise, they will be a thoughtful gift, but they will probably end up living in box or drawer with some other "thoughtful gifts."