I agree on the metabolism aspect, but the idea of brain temperature, while it makes some sense, fails to mention that brain temperature is merely secondary to the availability of the substrates oxygen and sugar to the scalp as well as the brain. If these substrates are readily available, more likely there will be higher metabolism that provides energy to heating the brain and to grow hair.
If, however, there is some bottleneck that limits the amount of sugar and oxygen delivered to the scalp, then hair growth would be negatively affected. I would say that the challenge really is to relieve these bottlenecks. Why is there low availability of sugar? Why is there low availability of oxygen?
Even if one has good sugar regulation, and has generally good metabolism, it doesn't mean the entire body is well supplied with sugar and oxygen. It only means that there is a higher immunity and higher survival characteristics, but it doesn't mean that the body's development is maximized. The body will consider its current state, and will prioritize survival over development. This means it will favor one going bald over one dying. It will pull resources out of supporting hair growth and put these resources to use to survive. It will favor putting the body in a less stressed state, where metabolism is lowered, than putting the body in an overdriven but highly stressed state. It will favor protective inhibition over destructive stimulation.
I would also argue that mention of metabolism varies throughout the body, depending on the environment and the state of the organ/tissue. In a very healthy body, the body would be firing in all cylinders, and optimization of energy would be very close or equal to the maximization of energy for development. In a very sick body, the body would be crawling to a snail's pace, and optimization of energy would be closer to minimization of energy production and expenditure in order to survive. And in between the two modes would be what most of us would be in.
I would see myself, for example, as having a mix of metabolic rates. Where my organ/tissue can support maximum metabolism, it would. Where it can't, it wouldn't. I can have normal body temperatures, and that means only that generally I can support a normal metabolic rate, and that maybe I have the necessary prerequisites to have a functional immune system that gets me through allergies and bacterial infection. But I have thinning hair, and that may just mean that my scalp isn't producing enough energy to grow hair. And that could be because it's not getting enough oxygen (or sugar) because the capillaries feeding the scalp (and perhaps the brain) are not delivering enough substrates needed to produce energy. It may be such that the temperature there would be lower. But lower brain temperature isn't the cause of low hair growth, but an accompanying result of lower metabolism in the scalp region.
I can only theorize on it but hopefully I can prove this in the next few months as I attempt to restore normal blood pressure through the use of proteolytic enzymes and if needed, cyclodextrins, to remove plaque from my capillaries. There is no way for scans to see plaque in capillaries, and so it seems we are operating on the assumption that what we don't see we don't believe exists. So, little mention is made in the literature of plaques plugging our capillaries, and thus limiting the delivery of nutrients to the parts of the body fed by capillaries, especially the watershed regions where there is no other supply but the capillary and where the body can't provide a bypass with new capillaries.
I believe when I'm successful at lysing out the plaque from the capillaries in my kidneys, my blood pressure will get back to normal. At the same time, I will also find my scalp springing new hair. If this happens, I will appreciate baldness to be an indication of a problem of plaque formation in capillaries more than anything else.
