As per my comments in the other mail, I think having a single file is difficult as we'd have to have a strict naming convention and/or your have a big hit searching for files during the load (which would slow down a UI). The format that I've described is however different to the OZW files in that the device files are (I think) largely self describing (ie some information is in both the product summary file, and the device files for exactly this purpose). The product file just provides a single place to look without having to search a set of folders for the appropriate device file.
I'm not against a single file if everyone thinks that's the best approach, but I really think that a top level descriptor file that describes and links the library is a better approach.

How is the version identified? I've not looked at this, but I assumed from what I've seen with the Fibaro devices that they change the Type or Id (since the same device has multiple sets of Ids). If so, the format that is currently defined allows this link to be made easily. If the version is linked separately to the Type and DeviceID, then we can add that for sure - completely agree here.