I agree very hard with your first two paragraphs. (Less so with the Imperial Radch assessment, but that's a long-standing qualm that I've basically given up arguing.)

I get that there's no good answer to whether to include nonbinary characters in a femslash meme (or event, or whatever), and I understand both deciding to include them entirely (e.g., femslashex) and deciding to exclude them entirely (e.g., femslashafterdark), but I really feel like trying to include some nonbinary characters and exclude others is taking the worst of both options and inviting a hell of a lot of potential wank.