Now before you say, "Well obviously they're coming soon, its October!", allow me to just mention that this soon might be a lot sooner than you're expecting! As with the Summer Game Loot Boxes, someone over at the console side of things has accidentally leaked the existence of Halloween Loot Boxes, the screenshots of which you can find over at ChronosHero's Reddit post.
So why is this significant? Well, the last time the Loot Boxes got accidentally leaked Blizzard released them within the next 24 hours, which means that if the same train of logic applies here as well we can expect to see Halloween arrive quite soon indeed. Naturally, all of this is pure speculation on my part, but the events are unfolding far too similarly for all of this to be a pure coincidence. Update: Alas, it appears that I was wrong, and since Blizzard doesn't update over the weekend the earliest we might be able to see these Loot Boxes is on Monday.
Since the screenshots are a bit too blurry to read properly, here's what the Halloween Loot Box description says:
"Celebrate Halloween with some frightening treats for your heroes during a new event : Overwatch Halloween Terror!
Trick out your collection by picking up Halloween Loot Boxes, available for a limited time*. Every Loot Box contains up to four cosmetic items, including at least one Halloween skin, highlight intro, emote, victory pose, player icon, voice line, or credits that you can use to unlock other items. More then 100 Halloween items are waiting to be unwrapped!
if your Halloween loot box contain an item that is already in your collection, you will instead receive coins!
*Halloween loot boxes are available to purchase or earn in-game until 11/1/16 at 4pm PT."
While all of that is fairly standard stuff, I've highlighted one rather intriguing part of this announcement - the mention of coins! This might not sound like a big deal given that Overwatch features an in-game currency that is very coin-like in nature, but Blizzard has always refereed to it as credits... even in this announcement! In other words, these coins might just be an event-specific currency that can be used to purchase Halloween skins, just as an extra way of ensuring that players get a couple of items they've really been gunning for. Without having to rely on random chance!
Once again, all of this is a massive amount of speculation on my part, but hopefully this ends up being true as the Summer Games Loot Box system was one of the most obnoxious way of handling new skins. Nothing will send a player down into a manic depression more than opening 100 Loot Boxes and not getting even a single item they were looking for... not that I would know anything about that! What I do know is that I have a great deal of faith in the Overwatch team, mostly because of how communicative they have been on nearly every topic, so chances are pretty good that my wild speculation might have some basis in reality.