Those ever talkative "sources from motherboard makers" are again flapping their gums to Digitimes, this time involving Nvidia. As the latest rumor goes, Nvidia's engineers are busy developing a chipset that combines the function of both a southbridge and GPU.
The funky dual-purpose chipset is Nvidia's way of sidestepping Intel's Sandy Bridge architecture and avoiding a potential messy legal battle. Intel filed suit against Nvidia back in 2009 claiming the license agreement between the two parties only covered processors that don't contain an integrated memory controller, which is the reason why you haven't seen any Nvidia-based chipsets for Nehalem.
Intel's Sandy Bridge architecture combines a CPU and northbridge into one, and as the story goes, Nvidia is hoping motherboard makers will opt to purchase Sandy Bridge without the southbridge (Cougar Point). That would save them about $15, which could then be used towards the purchase of Nvidia's combo chipset.