I really hate to be a downer, but I just cannot see a second fighter pass, or any bonus Fighters unrelated to the fighter pass. Being a longtime Nintendo fan has taught me not to expect more than what Nintendo tells you that they are giving you. Once Nintendo tells you a definitive number, that's usually it. If they don't have a definitive number, they just don't tell you. And to me, the five character fighter pass seemed pretty definitive. and I would double down on this dance since it's Sakurai in particular. He's not really a fan of season passes to begin with, and is tired of working on these smash games.
I think there is a decently sized chance that Geno is our last fighter. But I also think there's a decent chance the last two fighters may be somewhat underwhelming. Smash tends to front-loaded announcements that way. And if Geno isn't in the fighter pass, I'm just going to call it. I would be pleasantly surprised if they did announce him as a stand-alone bonus character, but I really won't be expecting it.
although regarding doomguy, I'm not sure he's as likely as we think, given that his support in Smash is fairly recent. I'm not sure when the planning phase 4 DLC started, but it was definitely before the game released, and doomguy didn't have much support until after the fact. Personally though, I would welcome him.