[Rudeofus]

Or is it the case that, commercial considerations aside, the likes of Kodak could have developed a satisfactory C41 process at 20C

I guess they needed a certain (high) rate of diffusion to make all three layers develop in lockstep, and 38°C was the way to go. AFAIK some color negative process(es) before C41 could be run at room temperature, but for some reason C41 proved superior.