I want him to be an opponent but I'm worried Oda will clown him like he's been doing with his antagonists lately including Admirals and thus Gear 5 will only make that worse too. I seriously dread Akainus future now.
Having him as an ally makes more sense to his character but the plot convenience and amount of allies for Luffy and Co is absolutely absurd, which had severe repercussions on the Yonkos and at least 1 Admiral so far.
Kuzan is a wonderfully written, nuanced character especially if you include Film Z and I really want to see him being more rogue, unpredictable, tormented, neutral rather than a cliche undercover agent. Admiral version of Drake even which doesn't bode well for him either potentially.
Kuzan as an opponent and thus being an obstacle would be far more interesting. He was disillusioned post Ohara and went from Fired Up Justice to Lazy Justice now. Now he's even more disillusioned and finally had enough, going rogue and joining a truly notorious pirates crew instead.
I believe he's had enough of following others, of having faith in others and hes only joined BB as part of his own personal agenda, he's not actually loyal to him. An iceberg sank the Titanic after all, Oda is definitely setting up some kind of parallel there too somehow.
I love the theory he joined BB to do what the Marines and WG have been failing to do, what the Marines have been held back from doing due to the oppressive restrictions of the WG, which is hunting down (other) pirates and take them down which he has generally has complete freedom to do so at least, as part of a pirate crew, especially such an "evil" and especially chaotic, self serving, power hungry crew.
Thus he may try to sabotage BB and Co too once he feels the time is right, maybe after learning more about him and their crew, especially their weaknesses and thus having their trust too somehow.
Also food for thought, Blackbeard was mentioned by Buggy as rumoured to never sleep. Back at Drum Island, Luffy mentioned hearing about people who can never sleep due to the cold.
Now a guy with literally the coldest DF in the series and thus a walking glacier/iceberg/absolute zero temperature etc is part of BBs crew. See where this is going? Also think about the iceberg and Titanic connection here too...
One more thing, Kuzan may have felt, the,WG was too focused on Luffy but ignoring BB as a threat way too much at Marineford and in general, hence snother reason he could have joined BB as part of his secret possible agenda to sabotage them and take them down.
I still prefer Aokiji/Kuzan going full rogue and maybe even supporting BB earnestly for whatever possible reasons. An Admiral defecting, going rogue and thus becoming an almost entirely unrestrained, chaotic, unpredictable pirate, with unclear motivations now especially makes far more interesting writing for me.
He's just as enigmatic as Kizaru is for be now too.
On a similar note, I'm kinda glad Fujitora is still somewhat antagonistic to the SHs in Stampede, not sure if he is Red but surely he must be too ofc?
Fujitora fascinates me and whilst I doubt he'll ever fully support pirates or the SHs ofc, he'll probs try to reform the Marines and even the WG somehow, after being inspired by them, along with the support and similar motivations and thus reasons as Smoker, Tashigi, Koby and maybe even Kuzan potentially.
But the Marines are still far more interesting as antagonists and should remain that way imo. Like a Garp and Roger situation at best.
Zephyr in Z, was a great example of a prominent Marine going rogue and thus antagonistic too and I doubt its coincidence that Oda had Kizaru and especially Kuzan encounter him and thus "deal" with him in different ways too.