If the OS/driver throws an error, or the motherboard/CPU/etc. were to fail, then all the GPUs connected to that rig would be down until you fixed the issue. Additionally, stopping at 8 tends to cause fewer setup headaches, at least with current Windows 10 drivers. (Without delving into more modifications, you're stuck with up to 8 from AMD and/or 8 from Nvidia.) YMMV with certain Linux distros.
Those are some of the main reasons why you should stop around 8 GPUs per rig.
I personally use the Asrock H81 Pro (2013 model), and it has worked fine for me. I can't speak for any of the other boards, though.
Thanks for your solid advise...
Yeh i am probably thinking to go with H81PRO BTC R2... low price as well..
Good thread, OP. I am doing the same as you now. The next logical question would be what power supply are you going to choose for that MB and which GPUs?
GPUs you can chose.. I am running 1080TI also.. 1070 Mini.. 1070 Extreme..
After MOBO Selection.. go to which cards you want to run.. than select PSU.
Some guys are also using Server PSU - HP ones.. i have to see how to connect GPU in to those..