NO SF can NOT download 4K from Netflix at this time.
Users also will need the top, most expensive plan to get 4K from Netflix, if SF ever can or does decide to support Netflix in 4K.
Asked: Why not? Answer: Only the SF development team knows why not.
Asked: When? Answer: Again, only the SF development team knows if or when.
The overall goal now, even right before V7, but now through all updates in V7 of SF, is to get as much as POSSIBLE available in 4K.
For some providers, it may not be possible; for other providers, it could get users an instant ban of their provider account.
EXAMPLE: Ban happy Amazon.