There's too little Ivan/By, but it is, in fact, the most common not-canon-het ship on AO3 (at least if you count all of ADS as one story.) But yeah, there's ways to read By/Rish as non-normative but the canon doesn't really emphasize any of them. The whole series is one of those things that was sort of very progressive when it started but I feel like, on that axis at least, the world progressed faster than the author.