For the sake of refreshing our minds in regards to the CacoMallow leak, here's a video showing the image leak, and the gameplay footage. You may mute the sound just to impartially observe and appreciate the image and gameplay.
https://youtu.be/1DFp_AXQTZg?t=17
Following from what Fatman mentioned earlier; the fact that Steve, Hero, Banjo, Geno, Ryu (Hayabusa), Waluigi, Lloyd, and Byleth were heard around 2018 according to Xenother makes sense not only in regards to the timing of the CacoMallow leak's appearance, but also the characters that did get added to Ultimate out of those.
So the characters (again) that were heard sometime in 2018 were:
- Steve (Microsoft)
- Hero (Square Enix)
- Banjo & Kazooie (Microsoft)
- Geno (Square Enix)
- Ryu Hayabusa (Koei Tecmo)
- Waluigi (Nintendo)
- Lloyd Irving (Bandai Namco)
- Byleth (Nintendo)
Do notice how some of these characters belong to the same Company. Considering this, within a Fighters Pass it would be "unfair" (perhaps) to include characters from one same partner Company. Ah, then in that case, among these characters most likely the dev team had to decide which of these would be added to the first Fighters Pass, while the others would be kept on hold depending on said pass' success. It didn't take long to realize that the first Fighters Pass was a runaway success with the surprise reveal of Joker (from Persona 5) kicking off as Challenger Pack 1; following with Hero, and Banjo & Kazooie as CPs 2 and 3 respectively.
For Fighters Pass (1), out of the names heard in 2018 the picks were,
- Hero (Square Enix)
- Banjo & Kazooie (Microsoft)
- Byleth (Nintendo)
What criteria they used in deciding which characters would be chosen for the first Fighters Pass remains an unknown variable. Luckily a second Fighters Pass came along and so far we've gotten another one of those names; Steve (Microsoft). Thus at the moment, the following names remain in the air,
- Geno (Square Enix)
- Ryu Hayabusa (Koei Tecmo)
- Waluigi (Nintendo)
- Lloyd Irving (Bandai Namco)
Huh, four characters; how coincidental (knowing there are still four slots remaining in the Fighters Pass Vol. 2). With Fighters Pass 1 however we got characters whose names weren't known such as Joker and Terry (although Terry started doing the rounds close to his reveal). In that sense, we should expect the same happening for Fighters Pass Vol. 2; the inclusion of characters that weren't head of way back then (in 2018), but have been doing the rounds much later (possibly near the date of what could have been their reveal).
With the other names that have been rumored around 2019 and onward, it's only a matter of adding them to the ones from 2018 and that's very much the speculation pool we find ourselves in at present time (and have been in for quite some time). Imo though, the names from 2018 should have priority over the later ones since most likely negotiations for them had already been made, and the others were done as well just in case (for additional passes).