In an interview with VentureBeat, Heroes of the Storm’s senior artist Phil Gonzales was (naturally) asked about whether or not Overwatch characters could debut inside the game, to which he responded in the affirmative. “We’re planning on bringing Overwatch heroes into the fold, but we’re going to let Overwatch have its party, and then we’ll be like, hey, they’re over here too.”
Gonzales also added that Overwatch would need to be launched first and enjoy its own time in the limelight first before being brought over, but that is something that will definitely happen. “What we’ve been saying, though, is that Overwatch definitely needs to have its own time to be recognized and celebrated. We want to let that happen. […] We have a soft limit of, say, six months before we’ll do anything like that. But we absolutely will be visiting Overwatch and bringing Overwatch into the nexus. Our past games and future games are all viable candidates.”
As it stands, it is unclear as to when Overwatch will be released. Given Blizzard’s history and habit of taking their time with their games, it might only be in 2016/2017 before we see it, although based on early gameplay footage we’ve seen so far, it certainly holds a lot of promise.