That it's built under Windows strikes me as quite an unusual feature. To their credit the developers provide sufficiently detailed build instructions that aren't too hard to follow. However the build environment is very specific. VC has a lot of configuration options, so no doubt very close attention is required to make sure everything is set up correctly.
Running the compiled system in a VM is sensible, kind of a shame though that Windows native Hyper-V isn't supported. Perhaps that will be possible in a later iteration of the OS.
Would be nice if the authors gave a rundown of how this OS compares with others out there. Without having a clear idea of this OS's features and advantages, potential contributors might feel hesitant about investing time and energy in its development.