Blizzard keeps adding new content for Overwatch, including new playable heroes. The last time players were sure: all teasers indicated that Doomfist would make its appearance. This was not the case since last month, it appeared to be Orisa. However, it could be that we don't need to wait as long this time for the next hero, because director Jeff Kaplan says that the new character is in an advanced development stage.
Other than that, Kaplan won't say much more about the new hero. Even the gender remains a mystery. It could be possible that Doomfist is coming to Overwatch soon, but it may as well be a completely different character.
"Yes! I absolutely know who the next hero is going to be. The next hero is very far along in development, so we’re at the point where we’re doing art for that hero, we’re doing a lot of aggressive play-testing. We know what that hero, what the abilities are and how they interact, so we’re at that point."
Blizzard employees have already played the new hero. Hopefully we don't have to wait very long for the official unveiling.
Regarding other heroes which Blizzard wants to add, Kaplan says there are several characters beyond the concept stage. So for now we don't have to fear that the collection of playable characters will get bored.
If the past is any indication, Blizzard will be teasing us mercilessly with the new hero. When they will begin doing so however, we don't know yet. We do know that next week the Omnic crisis event will take place in the game: the first event in Overwatch which has no connection with our own world. The Omnic crisis will start on April 11, so it could just be that we are going to get more clues from that date on the identity of the new hero.