This is an interesting idea and I think it has merit, but at the same time it’s important to consider broader variables.
The notion of guiding intensity by relative hunger could work if you were able to anticipate that hunger before it strikes. For example, even if you start a workout at a high intensity you likely won’t feel the need for exogenous calories until at least 45-60min in. For a lower-intensity session this could be true for the first 2-3 hrs. As such, your perceived exertion won’t have the nutritional-demand metric to rely upon for guidance and adjustment.
Additionally, much about how you feel in a workout – high or low intensity – with regards to nutritional needs will come from your diet pre-workout, either from earlier in the day or even the day before. Have you been calorically deficient and under a high training load for several days? If so, even a low intensity workout may have you craving that Snickers bar in your pack within the first 20min (what?! You don’t carry Snickers bars??). Conversely, you may have been eating quite well and resting a lot in prior days, so the effort of what should be considered Z3 actually feels quite mellow through the lens of the caloric input paradigm you described, and you may mistakenly run what is supposed to be an aerobic training run at too high an effort.
I’m not disguising my bias very well; i think perceived exertion, whether via nutritional/hunger measures or simply how the muscles and breathing feel, can be useful data but should be paired with the relative objectivity that a heart rate can offer. If the goal is to be limiting caloric input to only when needed, you can still accomplish that, but at the same time you may save yourself some frustration by better gauging what the actual workload on your body is during a given workout.
Hope that’s helpful!