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This looks like a really interesting addon, I do have a question though.
I recently downloaded a large number of assets from a renowned vendor. These downloaded .blend files contain one asset each in the case of trees and multiple assets for grass and small bushes. Now appending the assets all into a single file would be a massive overload of objects, considering that this library is 35gb in size. Since the files are structured to only contain the necessary objects (no cameras nor lights) and only the materials assigned to the objects, would you be able to batch mark all objects within a folder as asset? That way, I could see the previews in the asset browser and drag and drop the assets, without manually going over the 300 files and the individual assets.
E: This addon should be up to the task of batch marking assets from other blend files: Batch mark assets and generate previews from library files