"If you plan to purchase one of these motherboards for a new Kaby Lake CPU in the future, you will want to make sure that it supports Asus’s USB BIOS Flash Back utility. The utility will enable you to update the BIOS without a CPU or RAM installed. Otherwise, you will also need to purchase a Skylake CPU to update the BIOS, assuming the board doesn’t come with the update pre-installed."
In other words ASUS BIOS updates is a messy minefield. All the boards should support this Asus’s USB BIOS Flash Back Utility. If they can make a board that accepts BIOS updates without a CPU or RAM it should be universal. Even when Kaby Lake is finally available. If you wait to buy a motherboard which is supposed to be designed for the CPU. You have no guarantee that it will work.
This is the sort of thing that makes less knowledgeable people blow hundreds of extra dollars on an OEM computer rather than a cheaper and superior one they build themselves.