I like the idea of cooling the GPUs from the bottom.
But the design is flawed.
The fan is basically blowing air from the bottom on the GPUs, and then sucks that air back in.
So all you've managed to do, is recirculate the air via a slightly longer path!
It would have made more sense, if a fan and channel system existed, that routed open GPU cooler systems, to the open slot bracket; since most GPUs use 2 to 3 slot size cards.
This system is pretty useless in an enclosed case.
At best if one could reverse the airflow, and have the pipes suck the air out, and rout a hose to somewhere out the case; but these blower style fans do just that. They can't significantly reverse the airflow when the motor is rotating in the opposite direction. https://www.evga.com/articles/01168/evga-x299-dark/