For quite some time now, fans have been expecting Overwatch to eventually add the character Echo to the game. Blizzard has made it clear that Echo is an important character who is going to play a major role in the lore, but nothing too substantial about Echo has been released to date. However, it looks as though that's all going to change come BlizzCon 2019 on November 1, as leaks indicate that Echo will be revealed as a playable hero for Overwatch 2.
The big Overwatch 2 leak from ESPN claims that Echo will be hero 32 for the series. It's unclear if Echo will also be added to the original Overwatch as a playable hero, or if she will be exclusive to Overwatch 2. We should learn a lot more about Echo and what role she will play in Overwatch 2 come BlizzCon, but in the meantime, we do already know some minor details about the hero.
Echo appears in the Overwatch animated short Reunion, which sees her being transported on the Route 66 payload. She is reactivated by McCree, who tells her to join up with Winston and the rest who have decided to reform Overwatch. We don't learn much about Echo from the short, but we should learn more come BlizzCon 2019.
Another interesting detail about Echo that some Overwatch fans may not have realized is that she has been in development for the game for quite some time. Originally known as Iris, Echo was part of the initial pitch meeting for Overwatch, and she was based on concept art from Blizzard's canceled Project Titan project. Echo's original abilities when she was Iris were Particle Beam, Speed Boost, and Shield, which her Wiki page speculates were given to Zarya and Lucio.
When Echo is properly revealed for Overwatch 2, it's likely that she will have much different abilities than what was originally pitched. Overwatch heroes go through multiple iterations before they're released, and since her original abilities have been given to other heroes, they would be redundant. We should find out more about her abilities and lore come Overwatch 2's reveal at BlizzCon 2019 on November 1.
Overwatch 2 is rumored to be in development for unspecified platforms.
Source: Overwatch Wiki