...Can we please not use Linux and IoT in the same sentence. Linux is a wonderful OS. Most IoT devices are a world apart from what Linux needs to live. Most IoT devices are limited to 8k or 16k. That was not a typo - EIGHT KILOBYTES! Even if these little devices have an ARM M0/3, they do not have a memory manager. Many IoT devices have real time requirements and as blazing fast as Linux may be, it was just not architected to meet hard real requirements. Real world, mass produced product are under such extreme cost and/or battery constraints that pennies matter when selling at Home Depot or Target against $13 alternatives. Real world product have to live with one little processor to run the entire RF stack (BLE, etc) AND run the application, all of this in say 8k. Sure, there are exceptions such as smart phones, but how many millions of people are going to pay $800 for a thermostat (a few nest customers excepted).
/Rant Mode off
There is certainly a place for tiny Linux based computers in IoT home projects and as mini PCs and servers, as Orange Pi's home pages suggest. They are an amazing amount of technology for the money, just not scaleable.