IMHO only, I really hope people are careful doing this. Is it actually even truly a legal thing to do? A moral thing to do after one fish? I ponder, and what follows is just my 2 cents.
Handling fish and doing these kind of studies is at minimum, a stress, at worse, can easily probably do mortal harm. We all know to do this you'd need a good grip on the fish with one hand while the the forces a hard siphon down the soft tissued throat to steal a half days worth of feeding. You will see about 98% of content smaller than anything you could match with a hook, normally, anyway?
Besides, the fish was caught on something that just worked, right?
I do understand that part of the fun of flyfishing, versus slinging powerbait or a spoon, is that we are trying to find a more creative way to fool a fish with a natural imitation, but I am really from the school of thought it is location, location. Location. Having the fly be where it needs to be, placement and presentation, and not so much the pattern. Give me 12 different size Teeny nymphs in sparse to heavier pheasant tail, get that fly to swing, suspend, or dart at the right spot, you are in business. Might not be as fun as matching the the hurl color of a chironomid pattern, but probably near equal in results.
I worked in the field for an ichthyology lab where we sampled fish mostly by electroshocking from a boat, and we took a calculated proportion of a population, euthanized different age classes (guesses until later), took the stomachs out and saved in formalin. Then we spent all Winter huffing that formalin infront of binocular microscopes, doing detailed identifications and counts of what was eaten.
It is fun to see, and like everyone here in our youth, we did it on dead wild fish when we used black roostertail spinners and double spinners w/worms. Not sure what we were expecting to find, but finding a dead bullhead/sculpin in the belly of a 12 inch cutththroat, illicited an "oooh' and "ahhhh" that these were not just little fly eaters.
Just hope it is within reason and the fish health is primary. That said also, this is usually a planted lake scenario, so not damaging to a wild fish, I understand that. Native stream fish, this should be a total no-no, legal or not.
Last thing, you know aliens are watching what we do, and do we really think the anal probings was their idea in the first place? : )