It would also help reduce cost and complexity of small form factor and embedded systems.
About the only thing missing is 10GBASE-T Ethernet on the motherboard to perk up physical network performance.
USB 3.0 is backwards compatible but USB 3.1 now adds a new incompatible C connector that will take time for chassis vendors to deal with. Most likely a pair of USB 3.0 ports and a single USB 3.1 port until new chipsets with more ports become available.
I use PCI Express Wi-Fi cards with my boards now, they work fine. The ones I have now are older n300 and newer models now have ac1750. PCI Express x1 slots maike sense for Wi-FI as the technology is still evolving relatively quickly.