The only long term viable approach for IoT security is to not allow these devices on the Internet in the first place. Have the WiFi Access Point, or some other gateway, act as the broker for all information, and the default is each device sees nothing until given permission. *
Whenever this comes up people raise the point that this won't work because it disincentivizes making devices to slurp data, but it's not like that ecosystem actually exists at all, with the exception of smart TV which hardly counts as IoT. Consumer IoT hasn't taken off because consumers are rightly paranoid about bait-and-switch and being left with useless devices in the walls of their homes.
* This is roughly what https://github.com/atomirex/umbrella is trying to head towards, hence seeing if a $50 AP can act as a media SFU, and learning it totally can.