There's been a lot of talk about an Overwatch character appearing in Super Smash Bros. Ultimate over the past couple of months, which preceded but has only been strengthened by the announcement of Overwatch on the Switch. Now none other than Overwatch's Papa himself, Jeff Kaplan, has weighed in with resounding support for an Overwatch character to 'Join The Battle.'
When asked by an interviewer at IGN, Kaplan stated that he would be happy with any one of the members of Overwatch's current roster of 31 representing the Blizzard franchise in Smash. However, if forced to single out one hero, Jeff picked Tracer, who seems to be the general consensus pick among Overwatch/Smash hopefuls, due to her role as the face of the franchise. Jeff also acknowledged that there's a strong case to be made for Doomfist's fighting game-inspired moveset translating smoothly into, well, a fighting game.
Wes Yanagi, who is the principle producer behind the upcoming version of Overwatch on the Switch, agreed with Jeff (and plenty of others) that Tracer would be the natural choice, but threw dark horse Winston into the mix as well. While Winston may not currently be one of the more popular heroes among the Overwatch roster, especially since the demise of dive meta, there's something to be said for his role in the game's lore as the guy who gets the gang back together in the opening cinematic.
The closest glimpse to what an Overwatch/Smash crossover might look like comes courtesy of Reddit user ajfis3, who posted a highly-upvoted mockup of what a revamped version of Smash featuring only Overwatch characters would look like, including actual gameplay from a mode he designed in the Workshop to mimic the Nintendo franchise's iconic gameplay. It works surprisingly well, given the inherent awkwardness of translating moves meant to be used in 3D onto a 2D plane, which is the same challenge that would be presented to the Smash developers with the addition of an Overwatch character.
The Fighters Pass DLC pack released alongside Smash Ultimate still includes one character that has yet to be announced, who will follow the addition of Fatal Fury's Terry. However, the most recent Smash announcement confirmed the addition of characters beyond those initially guaranteed by the Fighters Pass, so there are between two and... theoretically an unlimited amount of chances for one of these characters to be Tracer, Doomfist, Winston or another beloved member of the Overwatch crew.