Yes I think for most people fat burning peaks around 50-70% Vo2Max and falls off again, whereas glycogen burning rises steadily to V02Max. In relative terms I think fat burning can be 65% around 40-50% VO2Max, easy walk pace, and might still be 30% at 70-80% VO2Max, half to full marathon pace. At a fast 1 hour run pace its pretty much all glucogen. The other variable is how much glycogen you have and how high your blood sugar level is. If you are topped up on glycogen and blood sugar your body will burn relatively more carbs even if you are walking or sitting around. Conditioning plays a role also, as your muscles can get relatively better at storing and burning carbs or fats or both depending on what they are used to. Digestion would play a role on long hikes. I can see some merit in higher carbs at breakfast and through the day, and more balanced at the end of the day where you have time to digest through the night. This should keep you warmer through the night also, especially towards morning when it is usually coldest.
At 15 miles per day, with say 4000 feet cummulative gain, an average person, somewhat overweight, might have to hike 8-10 hours but at a moderate pace. I think that would still keep them in a range where they would be burning more fat than carbs, but a diet somewhat higher in carbs would make sense if body fat is being burned along with dietary fat.
For yourself if doing 30-36 mile days, and perhaps 8000 feet cummulative gain on top of that, you gotta be fit and lean, and well conditioned to maintain perhaps 60% VO2Max. You should still be able to burn at least as much fat as carbs, especially when you round out the rest of the day, but I can see how you would need to keep resupplying mostly carbs through the day because even though you have relatively higher glycogen reserves they are a smaller percentage of your daily calories burned. Also, digestion is harder at 60% VO2Max than 40-50% VO2Max, and so mostly carbs while hiking makes sense. Still at the end of the day I can see a more balanced diet making sense. All in all I can see your diet being somewhat higher in carbs than fats, mostly for digestion reasons.
So a slower overwieght hiker and a faster fitter leaner hiker might have the same diet in relative terms, perhaps 10-15% protien, 25-35% fats, and 50-60% carbs, but for different reasons, and different quantities. The slower overweight hiker, like myself, might only need 3000 Calories of food, and lower in fat even though he is burning more fat, because an additional 1500 Calories in fat can be coming off the body. The faster fitter leaner hiker might need 6000-8000 Calories of food, lower in fat mostly for digestion reasons, and also because he is averaging a higher percentage of VO2Max. The slower hiker is burning more calories per mile because of his weight, but the faster hiker burns more calories in total because of their fitness. Now if a lean hiker decided they wantesd to slow down, even just 80%, they could burn alot more fat in relative terms, and probably be able to digest more fat also. So slowing down 10-20% in speed and miles per day might be a good option for lean hikers worried about losing too much weight, rather than taking zero and nero days and binging in town. Not sure.