I don't want to make any jokes in this post, because doing so would make me feel like the rubbish, nervous compère trying to entertain the crowd before an amazing comedian, for instance Bruce Forsyth or Jim from Neighbours, comes on. TF2 is a funny game, with funny promotional material around it. It is definitely funnier than I am. Funny like a clown, yes. For instance, this comic, heralding Valve's shootybang game's mysterious but surely impending Halloween update. By page two, it's triumphed with its concept of 'toilet wine.' On page five, it's got bald ghosts pinching each other's noses. Then there are raccoon sanctuaries, and wills made of human skin and... And, well, yes, very good.
There's also a teasing mention of portals to the nether realm, which may or may not be the next big thing in TF2 itself.
All the TF2 blog has to say on the matter of game updates is "Something is coming, everybody. Not "right now" coming — but you know, we're working on it." That perhaps implies that an All Hallows' Eve release date for said something may have been the victim of Valve time, or maybe it's an ARG for Half-Life 3. After all, the title of the post and comic both is 'grave matters', and people are killed in Half-Life games, therefore presumably going to their graves. I've definitely cracked this.
Most likely it's a temporary in-game event with spooky bosses, though. They always do that.