Reason number 437 I wish Valve would release more games: they're so good at packing them with brilliant little things.
(Warning: this post gets kinda NSFW. I know, I'm surprised too.)
It all begins with Miss Pauling. Miss Pauling, for those who don't know, plays assistant to The Administrator, aka the in-game announcer, aka one of the most powerful figures in TF2's long-running (mostly through comics and short movies) story. While The Administrator is cold and detached with moods that vary between pretty evil and entirely evil, Miss Pauling is a little bit nicer. Scout has a big, fat crush on her.
Fans have noticed that, pretty much since her inception (she came along later in TF2's lifetime), Miss Pauling has carried a writing implement and something to write on. It's kind of her trademark. In the new Gun Mettle update, this continues to be the case. Very talented Source Filmmaker, er, filmmaker Uberchain points out that she's holding a "top secret" file on the update's main menu screen — a clear reference to the contracts that form the update's backbone.
Things with the words "top secret" on them are, as we all know, the literal fucking devil. As curious-to-a-fault ultra monkeys, we must know what's inside or else we will stop eating and sleeping and eventually revert to a state of primal faeces-flinging warfare. Luckily, even though Miss Pauling's dossier is too blurry to read, Uberchain put two and two together. Waaaaay back when, Valve put out one of their infamous "meet the" videos for the Spy. It contained a running gag about the Spy's salacious (and hilarious) affair with Scout's mother. At one point in that video, Spy produced the exact dossier Miss Pauling is holding. It read, "Scout's mum." Its contents? Ummmmmm...
Uberchain even dug through Source Filmmaker's files to verify that, yep, it's that exact folder.
So that's a little weird, seeing as Scout is super into Miss Pauling and Miss Pauling is maybe... into Scout's mum? Or it could be a silly gag that means nothing. Regardless, it's one heck of an easter egg.
But OK let's get real for a second: it's 2015. I'd ship 'em.