Datamining is a potent practice. Either during development or simply a kind act to help spread the download size of a series of patches, developers may leave traces of future content within game files way before they're set to be properly revealed. If they're hidden, they'll be found. And that's exactly why Overwatch players are psyched for Christmas.
Spoken in detail over on Reddit, various sound effects and character interaction files have been shared on the popular message board; all of which point toward an impending Christmas holiday event for Blizzard's massive shooter.
Though it likely won't come as a surprise due to the various celebratory events to arrive in Overwatch over the last few months, leaks always get the job done when it comes to hyping up a crowd who usually know what to expect - but don't know when to expect it.
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Through the leaks, there's also the presumed Christmas jingle for your early listening pleasure. Other sound files reference common brawling themes like Arena, Challenger and Gladiator, leading some to suspect a new mode might accompany the festive event.
Of course, it's all purely speculation for now. But considering the Summer Games event "drove record engagement and participation", it isn't too outlandish to expect something for the year's jolliest of holidays.