For now, this appears to be feasible.
And it will probably stay feasible as long as the number of people who do it is relatively miniscule. But economics being economics, we’re freeloading off the customers who hook their smart TVs up to the internet and provide manufacturers with enough revenue that they don’t care about us.
But should the practice become widespread and manufacturers notice a material impact on their revenues, or should growth stall and manufacturers start looking to squeeze more revenue out of customers, they will start embedding SIM cards in TVs that can’t be disabled, and work out deals with wireless carriers to have a private data channel as Amazon does with its kindles.
my 4K “smart” TV is the first I ever bought, and I believe the last. By the time I will want to replace it, I believe manufacturers will have closed this “loophole” and it will be impossible to keep a new TV from phoning home.