Talking about the supposed big thing Selebus was planning since year one...I honestly don't know how much it narrows it down.
If it has to do with any specific character, who is the one with the most potential to have some sort of reveal or event? it has to be something special considering it took the game years until Selebus felt now it is the suitable moment. At the very least, the event has to be almost to the level of Prime Maya going poof
Is it of emotional value? or of lore/story value? Will a character be perma killed and not reseted like Maya? Is it something to do with the Gods?
I don't know if we can narrow it down further by taking into consideration the character events next update, since most of them have other adjacent characters that could potentially make an apperance, but at least we can probably cross out: Osako, Wakana, Tsubasa, and Yuki
So what I have learned from writing all of this. Is that I have learned nothing. lol I ain't confident on any of my assumptions, it has been years since I last played chapter 1 of the game, I only played the very beginning again but because of the revamp long ago.