AMD X370 For Enthusiast AM4 Motherboards:
AMD X370 is the chipset for overclockers and tweakers who need robust platforms. This chip provides the ultimate low-level control to its users and delivers ultimate graphics card bandwidth. By bandwidth, AMD is referring to max PCI-Express lanes as this is the only chip in the stack that supports multi-GPU functionality. The chipset supports both, CFX (CrossFire) and SLI.
From the same article. It appears AMD is attempting to either force the market or help kill multiple GPUs. Personally I think the time for multiple GPUs has passed given the power of the GTX 1080 and upcoming Vega 10 flagship, as well as the mainstream offerings being quite powerful as well, but it clearly eliminates Zen from any bargain machine, though it does appear that the FX-8300 series will continue to be manufactured...
It takes a very big chunk of silicon at 14nm to deliver good gaming at 3820x2160 and moving up to 7640x4320 will likely need 4-way even at 7nm