It also still increases the attack surface of the home by exposing your devices to a third party's network. You're now relying on the security of the network at the vendor to protect your device. What happens when
they get hacked? The question doesn't really change just because there's an APN instead of being being a firewall on WiFi. What happens when there's a vulnerability in the network adapter? Ultimately Why do I, the device owner, want my TV on Samsung's network? Why do I, the device owner, want my microwave on GE's network?
And, no, "software updates" isn't going to sell anybody on anything because current appliances already work without getting software updates. The only new reason many of these devices would need updates is because they're insecure devices on an Internet-connected network that need to communicate with the Internet. So they're connected to the Internet only to get updates to fix bugs and vulnerabilities with their ability communicate on the Internet. Are they paying Joseph Heller's estate for this idea?
And what happens to bandwidth? Let's say it takes off and everybody has 20 to 50 NoT devices. So everybody within 30 miles of a cell tower has 20 to 50 devices that want to connect? Some those devices are almost certainly going to be excessively chatty or poorly implemented, given the quality of most software. What happens when Samsung and LG release the new firmware update for their newest line of microwaves, washing machines, and refrigerators? Suddenly 20% of all house holds are trying to download 2 GB of data over the air?