Okay, this is something I was curious about myself.
I heard that XFX released these dual-gpu graphics cards, that are intended to be used for quad sli. There's a host of companies already selling prebuilts that use this technology (quad sli in 2 pci-e slots), so couldn't you take FOUR of these dualboard cards and stick them in a GA-8N-SLI Quad Royal for ock-sli?
Edit: here's a better looking image of the quad-sli.
I don't see why you couldn't jsut double that on a 4slot board?