Many smart TVs will connect automatically to any open wifi signal. Setting up a Faraday cage around the device, or a full Faraday room, isn't feasible for most people; likewise, disconnecting the hardware inside the device will be error prone and void the warranty.

Many modern televisions will stop working altogether of they go too long without phoning home. Some newer models won't allow you to use them without first connecting.

Likely advances in the future will be utilizing Ethernet over HDMI from newer connected devices, and perhaps building some sort of 3G or LTE or 5G antenna into the thing if the pricing and ad profitability works out. A more likely route is making agreements with ISPs to get access to their mandatory built-in modem wifi access points, which cannot be turned off by end users in some areas; that's a large logistical problem so we won't see things had that way for a little while.