I truly support your idea about "Infinity snap", but I think it would be better if mods can looking into the members profile and their post history before take any actions. I have looking in to that Reddit subsection and some of the members missed the snapping date(9th july 2018) due to unavoidable personal reasons ( but they all are not the shitposters) and they got banned. So if we going for this kind of system of banning (I believed we should) better to implement a system only filtered the real shitposters but not members who really cares about the forum. Some times they can be inactive some period of time due to personal reasons which didn't mean that they are spammers or shitposters.
One good member actually worth more than hundred of shitposters or spammers.
You really think someone would go through so much diligence if such a "snap" were to occur?
Did thanos look into the good deeds that Spiderman did before snapping him out of existence? Or any other superhero in the Universe that got "Shift-Deleted" because of the snap?
No.
So yeah, if this were to happen. It'd make the forum a cleaner place. But also a sadder one.