Couldn't a bit of this be dealt with through the "genre" tag? I mean the basics at least? By parsing the tag and choosing the EQ preset based on that?

Certainly, if the genre is a good enough indicator of what EQ one wants applied. If I ever implement something like this, it'll probably be flexible enough to say "when ID3v2 tag or FID field X is this value, apply EQ preset number Y" so I don't have to pick a particular tag or field.