It doesn't quite look like it from the pictures, but can this be moved far enough over to also use an ATX PSU?
If not, do you think you could offer a set of brackets that let you mount one PSU in the ATX slot, and another like you already have it?
Then people running 7-8 X 1080ti setups could get some relief
I think it would be easier/cheaper to just get a DPS-2500BB (which is what I use with it), which provides 2320w of power, more than enough for 8x 1080 TI's - running that dense with those cards in a 4U will probably result in heat issues.
After installing a couple of these, I suspect it would be difficult to do what you ask though, because the DPS encroaches into the PSU area (specifically the power cord which isn't small).