When I asked about subdirecties, I meant putting all books in the same subdirectory, because as tompe said in
this post (link) the directory lookup time increases, if there are a lot of books in the /eBooks folder.
But with the next firmware update maybe allowing browsing the library by directories, it would make sense to use different subdirectories.
I don't think, every tag should lead to a subdirectory. Maybe tags that start with a special character or are marked in some other way.