The debate around the Internet of Things and IPv6 will not hinge around how many IoT devices there will be (there will be a lot — many billions of IoT devices), but how those devices will communicate with the wider world, and what other kinds of devices they will need to communicate with.
In the scenario of a connected appliance that communicates with a manufacturer or maintenance provider, it does not need any IP address at all. It can communicate with, check for status updates, and download firmware, allowing for most control features, using your home Wi-Fi. It will never need its own address in this scenario. It will get one temporarily from your service provider while communicating with the back end (and this address can easily be shared with many other devices and computers across many other households) using common technology available today.
Now, what if my IoT device communicates with other IoT devices? The answers vary — if they communicate via Weave or Bluetooth while inside the home, this is all handled separately from the Internet and therefore also does not impact the need for IP addresses.
So today we have technology solutions that work and they function without the need for additional IPv4 addresses to connect an IoT device to a parent, peer, or the general Internet. Eventually, we will need to switch (whether because of IoT devices or some other factor), so how do we look at that need?
One way to evaluate the pressure to switch to IPv6 is to consider the market for IPv4 addresses. Cloud providers give us an interesting window into the cost of an address and what people are willing to pay for them.
At the time of this writing (8/15/16), Google will give you an IP Address (to host an app or website) for free, assuming that you make use of it. Other providers charge around $3 (Microsoft $2.98/month, Amazon $3.60/month) a month to use an IP address. These are low prices, even for consumers, and it seems clear that there isn’t much market pressure to switch to IPv6.
The conclusion is somewhat obvious, given the technical solutions above to connect IoT devices. At what point will the market push us to switch? At a price point higher than $36/year.