"PS – IMO, for practical purposes, the elevation effects on protein digestion/time of day stuff has a marginal effect, if any. Eat protein when you want it, when it's convenient, etc., and don't worry about those issues unless you're having some sort of problem."
While you're certainly entitled to your opinion, Bill, and Bradford equally entitled to take it into account, is it just that, an opinion, unsupported as far as I can tell by facts. The facts are that the thermic effect of protein is about twice that of carbohydrates and three plus times that of fat.
https://en.wikipedia.org/wiki/Specific_dynamic_action
"The thermic effect of food is the energy required for digestion, absorption, and disposal of ingested nutrients. Its magnitude depends on the composition of the food consumed:
•Carbohydrates: 5 to 15% of the energy consumed [6]
•Protein: 20 to 35% [6]
•Fats: at most 5 to 15 %[7]"
This has obvious implications for any activity, including backpacking. The heat generated by the catabolism of protein has to be dissipated by the body's circulation system, and the question becomes when is the better time for that to happen? When you're laboring up a slope to a pass under a blazing sun and already struggling not to overheat, or at night in your sleeping bag, when the warmth can be put to good use helping to heat your bag? A second downside to using protein as a substrate for energy is that it takes the stomach/small intestine longer to break it down. during this process, both organs will compete with the working muscles of the legs for blood supply. Also, protein used for energy is not available for tissue repair, hormone synthesis, etc, which is its primary function. For all these reasons, it is the body's energy source of last resort. While avoiding protein during the day when on the move, may apply less to a typical backpacker than, say, a competitive runner, it is nonetheless something for them to consider, and avoiding it for the most part can only be beneficial.
Some references on how the body's use of protein as an energy substrate follow:
https://en.wikipedia.org/wiki/Protein_(nutrient)#Aerobic_exercise_protein_needs
"Endurance athletes who exercise over a long period (2–5 hours per training session) use protein as a source of 5–10% of their total energy expended."
https://en.wikipedia.org/wiki/Protein_(nutrient)#Protein_function_in_exercise
"Protein is only used as anaerobic fuel when carbohydrates are low, or as aerobic fuel when lipid resources are also low. [7]"
http://livewell.jillianmichaels.com/proteins-used-last-source-energy-5473.html
"Disadvantages of Amino Acid Catabolism
Amino acid catabolism is the process of using amino acids as an energy source. Turning amino acids into molecules that can be used in the Krebs cycle takes energy, which means that burning protein for fuel is not as efficient as burning carbohydrates. In addition, your body needs amino acids to make new proteins. When amino acids are used as an energy source, it reduces the reserves of amino acids that are available for protein synthesis.
Amino Acids and Ammonia
Another disadvantage of using protein as an energy source is the byproducts of amino acid catabolism. All amino acids contain nitrogen atoms. When these amino acids are broken down, the nitrogen is converted into ammonia. Ammonia can be toxic when it accumulates in your blood, so your body has to excrete the ammonia through your urine. Although your kidneys can excrete moderate amounts of ammonia, if you break down too many amino acids, the increased ammonia excretion can stress your kidneys."
These are just to get Bradford, or anyone else interested in the subject, started.
For further information sources, use Google with the search arguments "thermic effect of protein" and "protein as an energy source". You will come up with more references than you will ever need to satisfy yourself as to where protein fits into your backpacking diet.