I've been thinking about the bar interaction between Kuzan and Teach.
There were clearly highlighted moments where they found they were more like each other than not:
Now let's consider Luffy and Kizaru.
Kizaru =
Yellow Monkey, with the color describing his power and the
animal describing his personality.
Now, what animal represents
Luffy's personality? A monkey.
While I don't think Kizaru will join the straw hats (can you imagine though LMFAO), I do think there will be a serious/significant character moment between them.