A lot of the speculation behind a second fighter's pass, as far as I've noticed, seems to be driven by one of three factors.
- Those who want First-Party DLC characters, as general consensus is that this pass will consist solely of Third-Party franchises. With the exceptions of Porky, Adeleine, and Sylux, they tend to tie into the next point as well.
- Those who want any of the following: a Spirit, a Mii Costume, a Pokéball Pokémon, a Boss Fight, or an Assist Trophy, as most believe that all characters in this pass will have had no Smash presence prior to this. It's also commonly believed by those who believe that Spirits are consolation prizes for rejected/unnoticed fighters that this would only apply to this pass, and in a second, anything goes (except generally multimedia/sometimes Sony/sometimes Summons and bosses).
- Those who want a character many consider pseudo-disconfirmed (Arle, Tails, Dr. Eggman, Crono, Lara Croft, Geno, Steve, Master Chief) by competition making it in. While nobody said there won't be two characters in the same pass from the same company, many believe this will be the case at least by coincidence if not a coordinated decision on Sakurai/Nintendo's part.
While objectively speaking, this wouldn't have an impact on the likelihood, I've noticed that many of the people bringing it up have at least one of these three in mind. I, myself, hit all three marks (Arle and Paper Mario). I don't intend to sound impolite or accusing others of pure bias, but much of the speculation surrounding it seems to be driven by an acceptance-denial fusion where people feel they don't have a chance anymore for this pass and want to move onto the next.
Part of it might be because we don't know a massive amount of what Smash 6 will do, and Smash 6 is scary to think about...
- We don't know if the game will have newcomers at all. At least a small group think it'll be a veterans-only club, but with a bunch of the veterans tweaked and changed around to varying levels of recognizability.
- We don't know if third parties will stay. The next game could be first-party only like 64 and Melee.
- We don't know how many veterans will come back. Having another "Everyone is Here!" is not impossible, but many are prepared for cuts ranging from a few to over half the cast being gone/demoted.
- Given that we won't get it on the Switch, we have to wait for until the Switch dies and the next Nintendo console releases. That could be around 2027, a LONG wait, and much longer than any individual game gap (Melee 2001 to Brawl 2008 being the longest at 7 years, but Brawl was intended for an earlier release which would've made it 6.) if we assume Smash 6 is a launch title for the Nintendo Placeholder, and we could be looking at a decade long wait. (And that would be crunching the clock given real life, but that's a topic for another time and place.)
- It would be extremely surprising if Smash 6 released for Switch, and outright bone-headed if it doesn't at least match Ultimate for features: it's destined to flop otherwise.
- We don't even know if Sakurai will be at the helm. Somebody else with a new vision might have different design choices that would mean our favorites won't happen.
I imagine this is what causes the concept of a second pass to even be in the topic at hand. While I initially believed in a long life cycle for this game's DLC, it seems that Sakurai is the kind of person who would rather just move on to the next game. Combine this with the fact that I very much believe that at least a bunch of the crew is done with working on Smash, given they've been since at least 2012, if not 2011, without any break, and the fact that Nintendo games rarely, if ever, get support beyond the first year, I wouldn't hold my breath for anything past this one.