I don't think that's correct. Win 10 build 1709 is supposed to work with more than 8 gpus. And the 8 gpu limitation in drivers was only relevant to amd cards. It was recently lifted as well and it's now up to 12 amd cards per system. And afaik nvidia hasn't had this sort of limitation in their drivers at all, it was the OS that was limiting nvidia users to up to 8 cards maximum, shouldn't be an issue anymore with 1709.