I could live with any of these but I really, REALLY like the fourth option. I'd suggest as well that if the ability to pre-collapse comments is added (as you say, for games/posts likely to grab triggery content/whatever) that the post author be able to specify a reason text for those when creating the post. So, if Joe creates a game post and turns this on, he could add "Auto-collapsed at comment time, due to nature of post". Then he could come along later, and if someone had said something that deserved a different collapse-text, change it.

If the user posting the comment can do this, need to consider: can they specify the text? (I think yes) Can they edit the comment to change that text? Can they edit that comment to change the text if the journal owner has changed the text? Things like that... Except on the first one I'm not particularly sure of the answers here.