Based on the content I've seen on this iteration of EC so far, I would say that the urge to make up rules is more dangerous to EC than the content that triggered the urge.
Meaning: No need for a rule that people can point to unless someone starts posting larger amounts of content that bothers some users. Let EC be neither SFW nor NSFW but remain in a superposition of either until there is an actual need for collapse.
Until then, I think we have a working EC-local common sense going on and the two booba-posters I have seen seem to accept the wishes of others to use spoilers in the future without needing a fixed rule.
There, I've said the same thing three times in different ways, please count that as 3 votes.
Also, in the absence of rules we can always resolve issues with classical power plays. If
>>8243 posts booba, and I don't want to see booba, I can react by posting depictions of whatever kinks that guy doesn't like until he stops posting booba (or one (or both) of us get banned).
I'm obviously joking, please no preemptive ban kthx <3