That's a very cool hack, but there are tons of things on a system that aren't the CPU that would benefit from some moving air. A fan somewhere in the system that just moves a bit of air would, I think, really contribute to the overall longevity.
Phones and tablets are designed for passive cooling. And not always well to boot, but you can at least assume they didn’t design for elements with ancillary active cooling.
The one tends to cause the other. There aren't any FETs anywhere in an iPhone that are passing 100A continuously. In any case, it's designed for that situation, whereas the Framework Desktop is designed under the presumption of the presence of a fan.
The whole black part of the case is for cooling if I understand correctly, so compared to your computer where the CPU can reach 90+ but the case stays at most warm, there the whole case reaches 70+ degrees.
Maybe a really mild winter; it's the same power as when I had my overhead light (2 60W lightbulbs) on in my room as a kid, and that didn't heat my room all on its own.