The recent Uprising event is just out of sight, but there's already a lot of speculation about a new Seasonal Event for Overwatch. On the quite popular subreddit r / Overwatch, some fans put time and effort into data mining of the Public Test Region, which resulted in proof concercing a new event.
What the event should accurately represent is not clear. There are some clues to new skins for Reaper, Tracer, Orisa and Sombra, as well as a handful of Sprays and Voice Lines from the other heroes. Some of these free-to-play content would be termed 'Event 6', which of course is a clear reference to the upcoming sixth time-bound Overwatch event.
In addition, the dataminers found references to new or alternative maps. For example, Nepal Sanctum would have a segment about "The Unfeeling Void", and King's Row received an extra long description that more closely reflects the background story of this level:
"Beneath the glamour of the ritzy King's Row neighborhood, omnics dream of a day they will have the same rights as humans."
The dataminer Failcraft, on YouTube better known as Hammeh, dropped a bunch of the collected results into a great speculation video about the possible upcoming event:
The general assumption is that this potential event must be a celebration of Overwatch's birthday. The game appeared on May 24 last year, and therefore Blizzard's immense popular shooter has become almost one year old. A Seasonal Event to celebrate that would not be world-famous for a studio like Blizzard.