I think an or function in the tag search would be quite useful, and it's the only thing furaffinity's awful tagging system has over e6's. Say you want art of raccoons or tanukis, sheep or goats, or in the case that is most common for me, are in the mood for art of similar characters or an entire evolution line of pokemon, but not necessarily limiting yourself to posts that have both at the same time. sometimes you get lucky, and two similar animals share a spot in the animal kingdom, But if you want art of either bandicoots or kangaroos all on one page, you have to search for marsupial and then filter out every species of possum and every other marsupial that doesn't fit the definition. If I'm in the mood for rabbit pokemon, I have to open several tabs because most people don't tag pokemon as the animal they're based on.
Sorry if this sounded like whining, I was more trying to lay out usage scenarios where such a feature would be useful, I don't even know if implementing a feature like this would even be possible with how e6 is laid out.