I started out hating this ship and now I'm kind of addicted -
First of all, the aesthetic. Two incredibly good-looking gals who look amazing together. Second of all, their personalities. Liar x detective? It's like Saiouma if Kokichi didn't simp over Shuichi and Shuichi actually had self-confidence. Celeste's whole thing is that she doesn't want anyone to see through her facade, and Kyoko, being the Ultimate Detective, is really the only one who stands a chance of doing that. Third, it's just so interesting. There are so many different ways this could go. Celeste is a criminal and Kyoko is the detective interrogating her; Celeste's whole persona is constructed around self-loathing and Kyoko helps her through her issues; Kyoko just gets curious about the girl with the weird hair and decides she wants to get to know her better. So much potential.
I didn't know what to think when I first discovered this ship. They barely interact in-game and would probably never work out canonically. But there are so many other scenarios where they'd work out perfectly. They've got compatible personalities - both reserved and closed-off but have entirely separate personalities from what they display to the world - and are just different enough that a relationship between them would be interesting. (Example: Kyoko is a secret sweetheart and Celeste has fabricated basically everything about herself.)
I'm not a huge fan of Celeste. She murdered Taka and Hifumi in cold blood by convincing Hifumi that Taka was a rapist (which, no, that's my son you're talking about, you can't do that) and doesn't feel a shred of remorse. She shows a bit of fear as she's about to die, but that's pretty much it. Her character, canonically, doesn't have very many layers. But that just leaves more room for interpretation, and there's a lot that her character could be expanded on - and a lot that Kyoko specifically could bring out in her character.
Also - mystery and intrigue with a splash of angst? That's my type of ship if I've ever seen it.
Never thought I'd say this, but Celesgiri gets an 8/10.