I’m not sure if you are familiar with Bookogs (https://books.discogs.com/) and Comicogs (https://comics.discogs.com/). Both sites together had more than 20.000 Users. 150.000 books and 50000 comics were added by the community.
Unfortunately the site comicogs will close at the end of the month and bookogs will close at the end of August. The database dumps (and the images) will be preserved and I think this is the chance to import them at bookbrainz. The data is available in json format. I know the structure of bookogs and I guess comicogs will be similar so I would like to support the import.
It can give a great push in data and the numbers of users might increase if they can continue without loosing their submissions.
What do you think?