ASUS has developed the ROG Xpander, an interesting new product that adds 4-way SLI support to the Rampage III Extreme motherboard. The PCB features four PCI Express x16 slots and two NVIDIA NF200 PCIe bridges to expand the 32 PCIe 2.0 lanes of the X58 chipset to 64 lanes. Pricing is unknown, but it's going to be quite expensive considering that just the two NF200 chips and an official 4-way license key from NVIDIA already cost around $100.
With Nvidia's flagship GeForce GTX 480 we have seen the ways of 4-way SLI and how it can break records like no other in the right hands. This is the reason ASUS developed ROG Xpander. The number of consumers that are interested in 4-way SLI isn't big enough to justify the added cost, but the extreme users should not have turn any other way but just upgrade to get 4-way SLI support with their ASUS Rampage III Extreme motherboard.
Judging from the information we have the reason for Rampage III Extreme not getting 4-way SLI from the start wasn't just the cost. The two bridge chips does enable higher bandwidth, but also higher latencies that most non-4-way SLI systems would be crippled by. Second generation PCIe x8 offers enough bandwidth to keep most users happy.