To be quite frank, proper speculation needs to have probabilities and observation on patterns in order to actually, well, speculate. Without trying to find a common thread amongst the additions and then compare those previously observed patterns to potential candidates, all we're doing is guessing and saying "I dunno, could be X character" over and over again. Speculation like this, especially when it lasts so long, is only really fun IMHO when you give it structure by trying to really look at the situation and form proper theories that have actual precedence to back them up.
Ok then I'll show you my thoughts on what I think will actually happen with the second Fighters Pass.
Trend seems to be that every wave of DLC so far, both in Smash 4 and Ultimate, that a couple of archetypes where more common than others.
One I'm certain of at this point is another fighting game character. We've had Ryu in Smash 4, Terry in the first Fighters Pass, and well, Min Min quite recently. A fighting game character has already been included, but there might be room for a 3rd party one. Ryu Habusa seems to fit the bill also, because the relation of Nintendo and Tech Koemi, and Ninja Garden being on Nintendo. He's my first prediction.
We also had a Fire Emblem character in literally
every wave of DLC. First Roy, second Corrin, and then there was Byleth. There's no new Fire Emblem coming out, that we know of... Unless something is saved for a Direct? Imagine this! A Nintendo Direct with a new Fire Emblem game for Switch, following up with a Smash trailer introducing the new main character. People would complain about it being a "anime sword fighter from Fire Emblem" only for the character to reveal it being something totally different entirely. Remember Three Houses did very well.
I'm not predicting a new Fire Emblem character btw, but I'd die laughing if it happens.
A 3rd party character with star power on Nintendo. Banjo is a good example, but Bayonetta in a similar way. I could easily see the likes of Travis Touchdown and Crash Bandicoot therefore. One fits a typical 3D platformer mascot as Banjo, with ties to Nintendo and a sort of history of rivalry like with Sonic. I'm not for Crash perse, but I admit he fits. Travis Touchdown has just a great timing. I'm sure he did well on the Smash ballot too. There's a new game coming, his first game was decently popular during the time of the ballot, and he's a character to appeal to a more adult fan base.
Breath of the Wild 2 has been in development for a while. There hasn't been a new Zelda character for long. And I cannot believe that Piranha Plant, Byleth and Min Min are to be the only first party newcomers. I can't even predict a character here. This is in the blue much like a new Fire Emblem character, however it's not based on previous trends. Just what I personally think as a possibility.
A populary voted character from the ballot, as Isaac or Geno. A definite fan favourite. I could see either happening with remakes of their home games. Both had popular games, and the Switch is amazing for RPGs. Both are more likely than people give credit for. I predict we get either of them.
Pokémon is also bound to get something. Seems most likely for the next newcomer actually.
Am now noticing myself basing my speculation about potential upcoming games. Makes me realize how hard this is without any news coming out. Starting to follow the leaks myself, even if I never believed them. Since I've speculated a lot of years already, for 2 games prior to Ultimate even, I always noticed how quickly public opinion changed after Nintendo Directs. So nothing being shown hinders true speculation.
In short; my predictions are: Ryu Habusa, Travis Touchdown, Crash Bandicoot, Isaac / Geno, and a new Pokémon.
