That's a new one ... ASRock will be releasing H110 Pro BTC+, which has 13 PCIe x1 slots for GPU. This board can mix AMD and Nvidia GPUs and the board has been fitted with extra Molex power connectors to add more power to the PCie slots. 

You will notice black and white PCIe connectors. The full size one is PCIe x16 gen, the rest is PCIe 2.0 x1. You can install just two DIMM slots with up-to 32GB of memory (DDR4) as well as an M2 SSD slot. There are 4x SATA 6 Gb/s. Gigabit Ethernet comes from the Intel I219V and listening to audio while mining apparently also was need as a Realtek ALC887-codec has been embedded. 

• ASRock Super Alloy
• Supports 7^th and 6^th Generation Intel Core™ i7/i5/i3/Pentium/CeleronProcessors
• Supports DDR4 2400/2133
• 1 PCIe 3.0 x16, 12 PCIe 2.0 x1
• Graphics Output: DVI-D
• 7.1 CH HD Audio (Realtek ALC887 Audio Codec), ELNA Audio Caps
• 4 SATA3, 1 M.2 (SATA3)
• 4 USB 3.0 (2 Front, 2 Rear)
• Intel Gigabit LAN
• Onboard Power On / Reset Button

ASRock To Offer H110 Pro BTC+ Mining Motherboard for 13 GPUs