ASUS are doing something very different to anything we've seen before with their premium X58 offering, the Rampage III Extreme. The board in itself is nothing all that unusual for a high calibre enthusiast offering of today; all the goodies and then some are in place; albeit, the lack of additional NF200 bridge chips for 4-way SLI action is a bit of a minus if a rich geek is looking to go all out.
However, that's where ASUS is doing something very different in conjunction with a separately sold ROG series product suited specifically to this motherboard which it calls the 'ROG Xpander'. This device is a daughterboard of sorts that attaches to the two full bandwidth PCI-E x16 slots on the Rampage III Extreme. It gives not one, but two nForce 200 bridge chips, pumping out two x16 links each to the residing four PCI-E x16 slots also on the ROG XPander.
In order to function, it requires a fair amount of additional grunt with connectivity for 1x 6-pin PCI-E power and 3x 4-pin Molex power; though not all of these may be needed for it to work properly, depending on your overall configuration.
You can also see in the images a decent sized fan, which aids in cooling the components on the motherboard underneath which would have otherwise been suffocated by this very large daughterboard.
ASUS also gave out a 3DMark Vantage screenshot of a system running in 4-way SLI with GTX 480 cards using this Rampage III Extreme / ROG Xpander combo. With the help of a Core i7-980X running at a whopping 6GHz, the system achieved a result of 52422 points.
Pricing on this additional piece of hardware? We're not certain yet, but given a couple NF200 chips on their own along with the required license would cost ASUS around $100 already, expect to pay 70%+ more off the shelf. But I'm sure that won't phase you too much if you already have the funds for four GTX 400 series cards.