It is a really interesting design and definitely something that AsRock had to do in order to “show muscle” after the competition in the crypto mining motherboard space started to heat up with shortages of the hugely popular AsRock H81 Pro BTC and other brands like Biostar announcing multiple new mining motherboards.
The AsRock H110 Pro BTC+ motherboard is pretty interesting with the 13 PCI Express slots available for use with video cards with the help of PCI-E extenders, but this also comes with some challenges. Initially we got information that the motherboard should work out of the box with 13 GPUs under Windows and Linux, and although that might be true indeed there seem to be some limitations. It seems that the 8x GPU limit is still a problem, however you should be able to run 8x AMD with 5x NVIDIA GPUs under Windows, but not all 13 from the same type out of the box (it could still be possible to overcome this limitation). For Linux users 13x GPUs do not seem to be a problem or at least thirteen ADM GPUs with the ethOS mining distribution.
Building a 13x GPU crypto mining rig could also bring some other challenges including problems with the power supply or to be more precise power supplies now that there are shortages and it is hard to source higher power models. Of course it depends on the type of video cards that you are using for your mining rig, but in general the new H110 Pro BTC+ crypto mining motherboard from AsRock seems to be more useful for builds that have mid-range GPUs and not high-end ones. Builds such as 13x AMD Radeon RX 470/480 or RX 570/580 that use single PCI-E power connector or Nvidia GTX 1060/1070 again with a single PCI-E power connector (sub-200W power usage) seem more reasonable. To help with the power supply limitations AsRock has even included a dual power supply adapter cable/module in the retail box, though for three or more power supplies you would still have to find another solution.
Imagine what a challenge it will be if you want to build a mining rig with 13x Nvidia GTX 1080 Ti GPUs. At 250W for 100% TDP per card you are looking at 3250W of power required just for the video cards, there are simply not much options for dual PSU setups that can handle that, so it is more at least a three power supplies setup. In this configuration it is not just the power requirements, but also the number of PCI-E power connectors that you would need for the video cards. You would need 13x 8-pin PCI-E power connectors and 13x 6-pin PCI-E power connectors, then also 13x 4-pin Molex connectors for the PCI-E extenders. You also need to be careful not to overload any of the power lines of the power supplies by connecting too much components on to a single cable.