I dont see much point in an 8pin cable - no ASIC hardware uses them, and most GPUs use only 6pin anyhow. The extra 2 pins are both black GND wires and AFAIK the GPUs with 8pin sockets will run fine with only a 6pin cable
They are designed for supplemental power to CPU's with 4 +12v and 4 returns. http://www.moddiy.com/pages/Power-Supply-Connectors-%26-Pinouts.html
Those are not the 6+2 PCIe GPU variants with the 2 extra returns in them.
And yes, I'd be interested in a few of them as well...
Ah - I suppose these could be made, but theres two issues:
1) cost will be about 30% higher (33% more wire, connector, and weight)
2) I really need a 100MOQ to create new cables. If anyone is interested in putting some deposit on at least 50 i could have them made, but from what ive seen the great majority of equipment is powered by PCIe.