Well, I am as of now doing 2019 part 1 on Windows 10 x64 with an NVIDIA GPU. The models do train fine and on GPU so far, I was only stuck due to some regex not working as expected on Windows paths. But together with a helping hand by akubodo on the twimlai slack I could get it to run and SGugger has already accepted my bugfix to be deployed with an upcoming version of fastai 1.0. So, I do think that Windows is a supported OS as of now. Maybe not a first class citizen but supported enough to get it to run. One can then later on either switch to a remote kernel on a Linux VM or directly to all Linux but at least it is not mandatory to directly switch the OS just to run fastai natively.