If they design it correctly, it will most definitely use all 20 PCI-e lanes, without switches, so it'll have better performance than the ATX boards, to boot.

Lanes 1-4: USB 3.1 Gen 1 to the back I/O
Lanes 5-6: USB 3.1 Gen 1 to header
Lanes 7-8: M.2 (M Key) for Wi-Fi card (Bandwidth to support upgrades to 802.11ax)
Lane 9: (Open for use on something)
Lane 10: Gigabit Ethernet controller
Lanes 11-14: Intel Alpine Ridge Controller (with DisplayPort 1.2 and USB 2.0) to the Type-C connector on back I/O
Lanes 15-18: M.2 (support up to 2280 PCI-e NVMe storage device or U.2 Hyper Kit)
Lane 19: Gigabit Ethernet controller
Lanes 20-22: SATA III (6 Gb/s)
Lanes 23-26: M.2 (support up to 22110 PCI-e NVMe storage device) on back side of motherboard
Here is a layout for something like this:
https://rog.asus.com/forum/showthread.php?53822-Thoughts-for-Skylake-Motherboard&highlight=skylakeEdit: For whatever reason, it won't let me shrink the image down