As @AllynCrowe and several others have mentioned, I think it would be great to see stories classified under multiple genres. Especially if "LGBT+" became a usable category. After all, "LGBT+" isn't a genre on its own.
I strongly agree with @solhawthorne about the fantasy genre here on Tapas. It seems to gather a very broad selection of stories. Having them split into subgenres like "supernatural fantasy", "urban fantasy", "historical fantasy", "magical realism" and so on would be very helpful.
Horror and mystery seems like they overlap a great deal as well. It seems to me a "Psychological" genre would do well to cover the series that seem as though they exist on the periphery of the two, or perhaps something akin to a "Thriller" genre? (Although now that I think about it, would "psychological" also include, say, a series dealing with mental illness? I think this would be an interesting tag, but hard to define?)