Spoiler tags until New Year's. After that, you're on your own.
Back in '02, we didn't have this problem. You beat Vice City in a weekend or you got left behind. The forum was the wild west and we liked it that way.
But GTA 6 is a different beast. 100+ hours, people got jobs, kids, whatever. So here's my proposal: mandatory spoiler tags for main story missions until December 19th (one full month after launch). Side content, easter eggs, random encounters? Tag those until January 2nd. After New Year's, the tags come off. If you haven't finished by then, that's on you. Stay off the forum.
A month is plenty. Anyone who really cares will have blitzed the story in a week. The rest of us can dodge the side stuff until the holidays are over. Come January, we're back to 2002 rules. No mercy.
What do you think? Too soft? Too harsh?