Kamikaze_Raven

Indeed and that's probably what I would recommend for the OP. The idea of reduced pressure loop is interesting but it's only use is shown in that video. Main problem is not being able to achieve lower temps than ambient and only advantage is not needing a pump and potentially better efficiency at the block but that's only in theory.

Yes that's right. You could even see it as reverse-refrigeration; normally pressure differences are used to force evaporation/condensation for cooling/heating, whereas in this system natural evaporation/condensation causes pressure differences, moving the fluid/gas so that you don't need a pump (kind of like how a heat-pipe works actually)

I'm not quite a refrigeration expert, but I'm not completely sure this is really a phase-change cooling solution at all.
 
In actual phase change cooling, your transporting a refrigerant between areas with different pressure levels. First the refrigerant evaporates in a low pressure area to absorb heat, then you pump the vapor into a high pressure area, where it's forced back to liquid, and therefore releases energy it absorbed when evaporating in the low pressure area. 
 
In this system however, the pressure is low throughout the entire machine. Sure the boiling point is lower, so it will evaporate, but the condensation happens simply due to the vapor being cooled in a radiator of some kind; you're not compressing it back into a fluid. This basically means the fluid will never get colder than ambient temperature. The key to real phase change cooling (refrigeration) is forcing the fluid to evaporate, mostly using pressure differences. Here, the fluid only naturally evaporates because of the heat from the cpu, and condenses naturally by the cool radiator.
 
Your idea would probably work, but it's just a very complicated and expensive way of doing something that can also be done with regular cooling. In fact, you might even just buy a phase change cooler, as that's cheaper and can achieve sub-ambient, and even sub-zero temps.

This was related to the CPU not being de-lidded as he said in the video. The GPU never got above 26C so it certainly works. The problem moves from getting heat out of the loop to getting heat from the silicon and into the water itself.

Air coolers almost beat AIOs at any price level and noise level. And air coolers are much much more reliable. I had one shitty corsair AIO failed less than a month ago. My AIO has been working for maybe 4 to 5 years which is probably considered very reliable among AIOs. But it still fails eventually. On the other hand, air cooler almost never fails. I think only custom build water loop can beat high end air coolers.

Air coolers almost beat AIOs at any price level and noise level. And air coolers are much much more reliable. I had one shitty corsair AIO failed less than a month ago. My AIO has been working for maybe 4 to 5 years which is probably considered very reliable among AIOs. But it still fails eventually. On the other hand, air cooler almost never fails. I think only custom build water loop can beat high end air coolers.