Just because households exist, doesn't mean they are untapped. There is a limit to Netflix's TAM. There are many households that 1) have no interest in screen-based entertainment, 2) cannot afford Netflix, or 3) do not have requisite internet bandwidth to acquire Netflix, among other reasons.Netflix is no where near that, there are still 2 Billion Households globally, that does not have Netflix.
Just last quarter, added 20 Million subs, 39 Million for the year.
60 Million Households ( out of 131 Million) in the United States, do not subscribe to Netflix.
Actually, having the NFL, might get that older crowd, that says Traditional TV is enough for them, I would assume they are part of that 60 Million Households that do not subscribe.
My point still stands that acquiring NFL rights is likely less about acquiring customers and more about it being a cheaper way of adding content rather than developing new tv shows.