I'm glad to hear that Fighters Pass Vol. 2 will be the exact same setup as Vol. 1: fighter, stage, music, and spirits. All of these conditions could be met by any character, so I don't think it helps or hurts us. People say that Fighters Pass wasn't a "fan demand" pass, but I disagree: at the very least, Hero, Banjo, and Terry fill gaps for regions and fan demands (Hero for Japan, Banjo for the West, and Terry for Latin America). Joker could be a "fan demand" character but that's a stretch, honestly. Byleth is clear Sakurai doing his "**** you, I get my Fire Emblem" pick. I mean, look at Ultimate's base newcomers: Inkling, Ridley, Simon (Richter), King K. Rool, Isabelle, and Incineroar. 3/6 are fan demand characters (Ridley, K. Rool, and Simon). So we have 6/11 unique newcomers as "fan demand" characters, and that's over half. I think Golden Sun's general resurgence as a whole coincided with the finalization of the Fighters Pass 2 characters, and Sakurai and team saw the social media storm following Golden Sun. They had to have, since it was nearly impossible to avoid while following general Smash news.
In conclusion, we are sitting pretty. While Assists might have meant Fighters Pass 1 was not an option, Fighters Pass 2 certainly still is, especially with the vocal and large demand Isaac has gotten (and sustained, that's key here). While other characters seem to rise and fall in popularity (Skull Kid, Sora, Dante, etc.) Isaac's fanbase is still large and vocal. Simply put, we might be in the best position of any character left. First-party, rights are already owned, large fan demand, Assist Trophy means that work wouldn't be entirely from scratch, and the fans were loud at seemingly the right time. The only other contender is Geno, and he has legal issues due to Square Enix (note I still think he'll join, SqEnix is just hard to work with, it seems).