Who knows, the only thing we know about the nika fruit is it makes the user laugh. Literally, his heartbeat alone sounds hilarious to him, which forces him to laugh.
Crack theory time. Smile fruits originate from Luffys DF.
We know Caesar made an artifical DF a Zoan specifically. Smile users can only laugh too like Joker gas from Batman's Joker got them.
Mayve Luffys awakening can make others laugh too potentially? Or its meant to since hes Joyboy ofc? But what if he can force you to laugh?! Or he can only laugh and not express other emotions?
Now Luffy has been retconned to a Zoan, I feel this might actually have weight to it.
Imagine Luffy being like the Smile eaters and can only laugh? So if Sabo is God forbid actually dead or Shanks/Garp/Dragon die, he can only laugh?
Its a repeat of Tokos situation but Oda may do it for the horror of it happening to a Straw Hat and especially not just any but Luffy himself too and thus not needing them to eat a Smile to achieve a similar scenario then?
Idk though. I don't want Sabo to be dead and if Luffy is being turned into a laughing maniac, maybe he will become Sadistic like how he clowned Kaido like a toddler playing aggressively but excitedly with a toy or unfortunately a pet in range too.
Oda could go full Looney Tunes or especially Who Franed Roger Rabbit here. Or even Meatcanyon somewhat lol.
Maybe not as extreme but something like a truly energic, childish, impartial God toying with their victims and going on whimsical rampage kind of thing?
It makes me all the more curious to know what Xebec was like and he compares in being a threat, in being complete anarchy and thus unpredictable and such too.