I had to laugh
Define a collection of subnets for the various IoT devices and assign DHCP ranges: it's dead easy to do and it'll help make things manageable. Most importantly, though, because you have subnets you can define access control lists (ACLs) to limit the traffic that can get in and out: ensure that the only traffic permitted is what the devices need to work and be managed.
And jost how do you explain this to the average punter with his 'smath' light switched, Central Heating and not so smart' fridge then?
And when you tell said punter that they need lots of expensive network kit (how many ISP supplied routers support subnets then?) in order to manage and keep his so called smart devices secure?
What you are saying makes perfect sense to those who read and comment on this site but for 99% of the rest of the population? Forget it buster.
 Especially deciding NOT to have any of this shit as I have did more than three years ago OR equally important, deciding NOT to connect the stuff you have bought up in ways that can make your network insecure.