Yup, I'm going to try to setup this first one to intake air from the front and do a test but the problem is you will push all that heat from the GPU's into the PSU, Board, Memory/CPU -- I'm not sure which is the lesser of the two evils.
The kit and its instructions however have the hot air coming out the front.
Just throwing my .02
BTC into the conversation. Unless the fans on the cards can be reversed, you almost have to exhaust out the front of the case. Otherwise the intake from the front fans and the exhaust (Facing the front) from the GPUs will just create some interesting thermal eddy's and not really move sufficient air in the first place. If you're really concerned with air-flow at the rear, you could also add a few of the pci-slot exhaust fans, like these:
https://www.newegg.com/Product/Product.aspx?Item=N82E16835119066I'm not recommending that one specifically, just using as reference.
The case add-on looks great, if I was getting back into GPU mining, I'd pick this up in a heart beat.
There is an option that reverses the GPUs to point towards the back. It's not a standard option but I requested it for an additional cost.
Currently all my GPU's face the back, Good idea on the blower fan, I didn't even think of adding those in as its been years since I've used them. Don't know if they will get in the way of riser adapters or not but I'm going to look into this option.
Edit: From what I can tell, these blowers will interfere with the PCIE 1x-16x risers. Bummer.
