I’d like to preface this by saying that the five DLC characters hinted at are likely just the first of many. Given Nintendo's plans for the Switch and how well
Ultimate is likely to sell, there will likely be a lot more DLC to come, especially with Sakurai’s statement that he intends to have this Fighter Pass completely available within a year
(the absolute madman).
The five characters of Fighter Pass #1 will probably not include any Assist Trophies or Mii Fighter costumes, as the five characters in Fighter Pass #1 are all currently in development and it will take time for the demand for Assist Trophies and Mii Fighter costumes to be upgraded to full playable characters to grow large enough and loud enough that Sakurai and Nintendo are likely to take notice. Also, Assist Trophies and Mii Fighter costumes are selected later in development than playable characters, and Sakurai does see being an a Assist Trophy or Mii Fighter costume as an honor rather than an insult, so the chances of any characters chosen as Assist Trophies or Mii Fighter costumes having also been chosen as DLC characters in Fighter Pass 1 are pretty much nonexistent. That means no Bomberman, Krystal, Isaac, Waluigi, Shadow, Zero, Lip, Rex & Pyra, etc. — they'll all have to wait for Fighter Pass 2 at the soonest. I also don't think that Geno is in Fighter Pass 1, as it may be seen as redundant to have two
Mario DLC characters in development at the same time. (I’m still having a bit of difficulty processing that we will be able to play as
a friggin' Pirahna Plant in
Ultimate, and that it was selected before Geno.)
I do believe that Banjo and Kazooie are in Fighter Pass 1, as I feel that
papagenos
' claim that Sakurai finalized a deal with Microsoft to get the rights to use Banjo and Kazooie at E3 is still extremely credible. This would be far too late to start developing them for the base roster (and I doubted from the start that Incineroar would have been dropped mid-development to free up development time for Banjo, as that would have been a boneheaded design move), but right on time to begin developing them for the initial DLC set. I also believe that a Square Enix rep is in Fighter Pass 1, as the reveals of Ken and Incineroar as playable characters and Isaac as an Assist Trophy in today's Direct have given Vergeben's credibility a huge boost IMO. Assuming that the rumored Minecraft content is a Spirit, it makes sense that the Square Enix rep just missed the boat for the base roster; while it's
possible that this is Geno (if his Square-rep status outweighs his
Mario-character status in Sakurai's eyes), it could also be a new-franchise representative, such as Chrono, 2B, or Lara Croft (heck, maybe it's Neku or Sora). Finally, I think a Namco rep is likely to be in Fighter Pass #1; Namco co-developed the game with Sora Ltd. and is kinda due for more representation. Heihachi, Lloyd Irving, and Klonoa are the most likely characters to occupy this slot IMO. And that’s all the predictions I feel like making.
EDIT: Hold on, I've heard statements that the DLC characters aren't decided yet and that development of Fighter Pass 1 will take somewhere around one and a half years. I still expect at least a second Fighter Pass, if not a third.