I'm of the opinion that Kinemon will likely join. Unlike Jinbe, I'm willing to accept arguments against him, and realize that my own theory is a bit out there.
I don't think Kinemon is Momonosuke's dad. I think that's a lie they created in order to protect Momonosuke's true identity while they travel. Look at the scenes around the "shogun game" that Nami, Brooke and Chopper played with him, look at the initial reactions he and Kinemon have towards each other. It's all a little bit off. I think that, when he and Kanjuro* get to Zou, and meet up with the third samurai who traveled with them, we'll have the full story which will lead us into Wano, and I'm fairly confident, that will lead us into direct conflict with Kaido.
And, I'm also of the opinion that he fits well into the crew. Two swords, Fox Fire style, Devil Fruit, self-denial gag and perversion hidden behind chivalry make him unique enough. Clothing arguments don't sit well with me when it comes to similarities, since the Strawhats have iconic outfits, but aren't sacrosanct like other series. For example, even when Goku studied under other masters, he always ended up in something that was basically the Turtle Hermit's gi.
*That reminds me! Remember when Kanjuro sent Kinemon and Momonosuke off? And when he reunited with Kinemon? His first priority in both cases was the safety of Momonosuke. His wording of his reasons is very suspicious.