You already know that IoT is a term used to loosely identify items that have been imbued with enough intelligence and communication abilities to send messages across the internet. First of all, this means that these items are not human in the ways we normally think of humans using computers to send information via the Internet. But that doesn't mean that some of these 'things' can't be humans, or at least humans carrying with devices that do the communicating for them. The connections and the information are triggered by conditions as they change.
That information is transmitted using some kind of message format. It's likely that the vast majority of those messages will not be in EDI X12 format. Some will exist in proprietary formats created to meet the specific needs of the devices, and I expect a larger portion will use some sort of XML format simply because of the ease of creating the content. But there's no reason that 'things' that are already part of the supply chain and would normally be encoded in X12 format documents could not be produced in exactly the same format and thereby easily incorporated into existing processes.
As one example, consider the various transport functions that could benefit from inclusion in the IoT. As RFID is becoming more available at different levels of itemization, the tags need to be read, and the data collected by reading the tags incorporated into messages. Typically those readings are done as items transition from one location to another, or as a person scans items or an area.
But it is conceivable that some of the things in the IoT include the carrier's truck, the pallet mover, the loading dock, and the shelf on the store floor. With the proper programming these things can be made to trigger events that create documents to update item status. These could include events like change in temperature or G-force in the truck, change in quantity of items at any point in the chain, and inventory counts in real time.
It's interesting to see how the individual pieces of this ongoing puzzle continue to interact and build capability as new functions become available. Feeding the data produced by the IoT into central storage and analysis engines will go a long way toward bringing real time visibility to the entire supply chain.