It appears that more content is on the way for Overwatch beyond just character additions and new maps, according to a recent investor call. A full transcript of the call can be read here, but the footnotes to the chat are that Activision Blizzard are viewing the game as “a huge tentpole franchise”, and that the company is focusing more efforts to expand the game than they had before that will still include new heroes, maps, and events. As to what those plans are exactly, the company didn’t go into detail beyond saying they would continue to focus on balancing out the current game while incorporating new content as they go.
In June, Overwatch will be approaching their Third Anniversary event, which usually is right around the time of E3 2019. So if the company had any big plans on the horizon before BlizzCon 2019, that might be the time to make some announcements and get the word out there. But again, Blizzard has been known to withhold info until the last possible moment and keep their cards to the chest until BlizzCon, so it’s more likely we won’t see much of anything beyond regular events and content until we get to November.