FWIW, the European Broadcast Union (EBU) rates cameras too. They have eight tiers, from 8K down to HD, from cameras certified for major production to B/C/documentary cams. One also has to assume, since EBU predates Netflix, that the rating is a constantly moving target because the once dominating 3 CCD models are gone and long forgotten. Under that notion, one also has to assume that Netflix, at some point, would start disqualifying the 4K cameras, as it moves up to 6K, then 8K*.
* This doesn't mean it'll quit streaming in 4K but that it will want 6K/8K files.
* This doesn't mean it'll quit streaming in 4K but that it will want 6K/8K files.