For those who haven't been following, the rumour is that NRS tried really hard to get Pennywise into the game, but wasn't able to secure the license and landed on Joker as a replacement guest character (likely due to how easy it would be to get approval in comparison). It was really disappointing to hear that Joker may be a guest, even more of a disappointment that he's ending up in KP1 to replace Ash.
And yeah, Ash not being in KP1 is strange. There's a chainsaw tease in the first trailer, he was datamined already, and...personally, the only guest character I'm interested in (though Terminator may end up fun if they go hard with the dialogue). I guess some people were assuming that Doom guy was replacing Ash, but...I don't know. I'm still expecting Ash later.