Yeah, they most certainly will. Although, I would be surprised if the next Smash wouldn't have all of the characters from the previous game (Smash Ultimate in this case).
I would be surprised if all the smash characters made it in the next game, 80+ character is a tall ass order, but they did say they plan to make smash ultimate last for 10 years, so maybe there wont even be another smash, and if ultimate is the last note they want to end on, i approve