It is not yet a requirement that 3rd party vendors include metadata, and I hope things stay that way. I think the creator of a product should have full control over how he or she packages it.

If metadata is wanted for a product that does not have it, installing the product, loading it, and saving it to the relevant preset file type, ie pose, chararacter, materials, wearable, or what have you will put it in your Smart Content directory, at least for DAZ Studio 4.x and 4.5 Pro. This works similar to metadata if it isn't metadata in actuality. I save poses, materials, wearable, character, morph, and even scene presets, and all of these appear in my Smart Content.