Given the connection between Sukuna and Yuji, I prefer him to be the final boss, not Kenny.
But if I had to guess, it would be Kenjaku. An even more powerful version, to be precise. How he'll get there I don't know.
Sort of agree. Kenny’s currently pretty strong but two or three grade 1 sorcerers with appropriate CT could take him down. His whole master plan is increasingly looking like “I want the world to give birth to a whole new kind of superpower Ed human/curse hybrid which I will then parasitically possess”.
JJK’s whole deal is repetition and variation of some of the more annoying macguffins central to the plot of Naruto. Namely immortality via body possession and as a means to facilitate multi-lifetime research into the nature of chakra/cursed energy.
Kenny’s whole thing is that he’s JJK’s version of Naruto’s Orochimaru. He possesses new bodies and gains their cursed techniques in addition to his own, while expanding the horizons of cursed energy knowledge via human experimentation. His current gambit seems almost like he’s trying to birth the JJK version of Naruto’s Jyuubi which he will then become the host of.
Sukuna is essentially JJK’s version of Naruto’s Uchiha Madara combined with the 9-tailed demon fox. Starting out as the “nuclear batter” powering Itadori Yuji’s newfound chakra on sorry cursed energy, he’s now become more like Uchiha Madara - history’s most feared villain, who’s figured out body-hopping himself in the same way as Orochimaru/Kenjaku.
Naruto kind of..punted on the whole “what is chakra” thing (powers gained from an alien tree’s fruit, at first used to supercharge human connection and empathy, later on used to supercharge human physical prowess).
JJK has, to me, spent more time contemplating the ramifications, origins, and future potential of cursed energy. While it’s calibre of plot and character writing has been overall far below that of Naruto, I’m hoping that it does a better job with exploring the philosophy of humans having magic that is essentially powered by negative emotions. (Funny enough that’s essentially the explanation in Naruto of how the Sharingan works).