I honestly think that Sakurai is going to step away after the five DLC fighters are released, and once he does that, I imagine Nintendo will stop supporting the game as well. While his joke about taking a break was obviously done as a laugh for his constant involvement, I do think it holds true that he doesn't just want to work on one game indefinitely. He's basically worked on Smash constantly since production of Smash 4 started in early 2012, and that'll have been almost 8 years by the time the DLC cycle finishes. He's going to want to move on to something else I imagine, and when Sakurai goes, I don't think Nintendo has the heart or even proper preparation to deal with his departure. He's too integral to the games at this point.
So, no, I think Sakurai leaves and they pursue other ventures at that point. A second season of fighters would make a lot of business sense, but I just don't see Sakurai sticking around for something like that. And if they're planning to have these characters release over the next year and a half almost, that'll support the game for plenty long enough I imagine.
I do think we'll see a little bit of content outside of the fighter pass. I could see them throwing in a stage or two extra, perhaps even deciding to include a new Echo fighter down the line just as they come up with things. They worked hard on DLC for Smash 4 and certainly went beyond the fighters with a handful of stage DLC. I know people want Pac-Maze back for example, so reworking that to include in the game could happen for example. Maybe even after this game's hype cycle we see them give an Echo out like Impa or even allow Shadow the proper upgrade from assist trophy as one. It's not guaranteed, but I do think it would make sense to see a little something extra.
