Blizzard has announced rewards for players who purchase the Blizzcon Virtual Ticket. Overwatch’s unlockable is the Sombra Demon Hunter skin. The skin currently requires you to purchase the Blizzcon Virtual Ticket. However, if you are not interested in purchasing the virtual ticket, the skin will be available at a later in 2019. If you read the official terms they say:
The in-game items for Overwatch, StarCraft II, and StarCraft: Remastered will also be available separately in 2019—further details will be announced at a later date
We are going to assume that the Demon Hunter skin will become available to purchase with Overwatch credits or available via loot crates next year.