Well, to be fair, it wouldn't be a discussion if I just put it in and ground it up... so that's no fun.
Traditional matcha stones are far larger than this grinder though, and will grind about 1 ounce in an hour. I will be grinding for a far shorter time more than likely... possibly 10-20x faster than they do, which will significantly increase the probability of burning the result.
Additionally, pre-refrigeration and nitrogen packing matcha from 'tea masters' would have been far lower quality than is possible today. In fact, no doubt the most elite matcha drinkers today would probably scoff at such matcha as very low quality. From a strictly chemical standpoint, the only way to get ultra high quality matcha is by controlling the temperature, humidity, and atmosphere. So while people think of the 'japanese master' as something out of mythology, in reality they are just people grinding tea in a sub-optimal condition
You make an awful lot of significant claims without backing them up. For one, while refrigeration makes sense to try and prevent over heating, matcha has a way of turning into goop-y dough any time it comes in contact with the slightest bit of water. I am worried that if any sort of condensation happens you will end up just making matcha play-dough or paste, which will likely taste far worse than matcha that got slightly too hot due to grinding. While you are grinding more and quicker than the machine stones, I doubt the stones will heat up significantly in that length of time (as others have said). In regards to your theory about shearing forces, I do not understand how keeping something 30-40 degrees cooler than room temperature would cause any sort of dent in the micro generation of temperatures on the scale you are talking about.
I get that you are doing this for health reasons, but most of us drink tea because we like tea, and not for the health reasons. We would rather drink something that tastes good than something that doesn't. While I am not saying this will taste awful there are reasons why you rarely see these matcha mills available, and why in all my years tea drinking I have only seen one store carry Tencha (which I believe discontinued it). I think if it were a good idea, tea drinkers are fanatical enough that this would have seriously caught on on some level. I would say people who appreciate quality Japanese green tea, are about on the same level as people who appreciate incredibly high quality coffee made at home, and yet there is a plethora of Espresso makers, and high quality coffee grinders available. And they are plagued with similar ideas of degradation of freshness as tea.
In terms of tea masters the intended goal was to get good tasting tea, they didn't much care about its "chemical make up" as long as it was tea. While we do not know if the new methods developed out of necessity to create the volume of matcha needed today, or if it actually tastes better. If the former were the case I imagine there would be a market for hand ground matcha. If the later is true, then isn't that sticking to the credo of the traditional teamasters?
I will end this lengthy post with a quote from our trusted moderator "Like what you drink, and drink what you like" and if I may also add "in what ever way you choose to make it."