I think that Steam is an interesting case in point here. For those unfamiliar, it's a service that lets you buy and download PC games. If you change computers, it's relatively easy to re-download games, or to delete them temporarily from your machine if you're out of space, and then download them again later (perhaps switching in and out of games).
I mention it because it's fairly hot about logins that are from different machines, or even familiar devices it's not seen for a while. You will commonly be asked to re-authenticate yourself via an emailed code.
But the point of this is that if you're using your connected TV Netflix app to nearly always watch Netflix, then you probably won't be asked to re-authenticate. It's only when they spot "suspicious" behaviour on your account that they ask you to do this. I reckon that if they're smart, they can flush out a few unathorised password sharers.
I suspect that it'll be a very subtle thing.
Don't forget the likes of Netflix are already discontinuing support on some older devices, so they are prepared to make life a little difficult for some of their users. And these companies are pretty smart about testing things amongst discreet sets of users or in specific markets. I'm led to believe that Netflix does this a lot. Try something, see what the reaction is, and then decide whether it needs to be killed, tweaked, or rolled out further.
Adam