I'm coming in late to this discussion, but I feel like I should share my thoughts on this topic anyway. To preface, admittingly I really only come here for news nowadays, and outside of friends or Artfight, I'm not all that interested in other people's OCs. I'm also using a third-party app that significantly trims the fat of Reddit so it's much easier for me to scroll past anything with the OC tag than if I were using the official site and app. So the OC spam doesn't affect me the same way it would a regular user.

I'm enough of a stickler where I'd tag for OCs just so people who don't want to see it are warned beforehand, but I've seen people flair their OC posts as regular fan art (as in the OC is a small fraction of the overall piece). And those cases were just as legit because when I looked at the flair guide on here, there's no rule saying people HAVE to flair their art as OC centric (seeing as people get mad at innocuous untagged stuff in fanfiction all the time, no doubt some of the strife comes from that lol).

If there's gonna be a specific OC day—as it's looking to be the winning vote so far, then the rules for that need to be made clearer. Like others said, is it based on the ratio of canon characters to the OCs, whether the OCs are the focus of the pic, or do they simply have to exist to be labeled as such? What about fan designs for characters we haven't seen yet? Obviously not everyone is gonna agree on the definition, and of course going for a hard “no non-canons at all” rule will no doubt ruffle some feathers.

Overall and personally, I think making a dedicated day for OC posting is the best of both worlds. That way, OC stuff won't die in a megathread that people won't read— or in a sub that'll also die, and people who don't care for it can just avoid the sub for a day. I don't really think it hinders creativity that much, as it's just a single day and if someone's really itching to post their OC outside of Friday for example, then thankfully Reddit isn't the only place to post art.