TV makers would have to collude with every ISP for that to be worth depending on.

Not to say it couldn't happen - but it wouldn't be a backdoor thing, it'd be very up front. All that's needed is for ISPs to create/join some SSO-like standard that lets you use ISP credentials as smart TV credentials (e.g. Your Xfinity account is automatically your Vizio account, sign on with your Xfinity account to get free streaming deals now).

I feel like if TVs start doing that, they'll display a network ID and signal bars at the top of the screen like cell phones do, so the TV maker doesn't get blamed for ISP problems.