Blizzard has stated numerous times in the past that an Overwatch 2 was not in the cards, but a recent report by Kotaku says otherwise.
According to anonymous sources and Jason Schreier's word, apparently an Overwatch 2 is currently full steam ahead and expected to be revealed at BlizzCon 2019. Though his sources didn't reveal too many particulars about this rumored Overwatch 2, it was mentioned that it will include a Left 4 Dead-style PvE mode and the usual event rotation that the current game has.
It's not too terribly surprising, despite the studio saying to the contrary, that an Overwatch 2 is being considered. The first game was met with record-breaking success upon launch, and despite its original intent as an MMO, it performed, and continues to perform, really well.
One thing that many current Overwatch players have been asking for is a single-player campaign. The report didn't include anything about that, but if it were not included that would be a strange move on Blizzard's part. Considering that's been by far the biggest request from fans, the continued dismissal of that would be a weird move to make, though hopefully they are considering a totally different approach to the game to make a sequel worth it, versus simply supporting the current Overwatch and adding more components there.
With an Overwatch 2 in the mix in addition to the push for Diablo 4, it's going to be a very interesting time this year at BlizzCon to say the very least.