I know there's the "all synced photographs" collection, but I have a need to create a smart collection based on various other criteria and I'd like to include whether or not the image is synced to Lightroom Mobile. Is this possible? I can't find any criteria to use for this.
I don't think there is any way. I've poked around the undocumented corners of the LR plugin SDK and couldn't find anything there, so plugins can't add this functionality either.