We’ll see, but I feel Oda may use him to further the big mom or CP plot line. It would definitely fit with how CP0 was just talking. We’ll have to see more of what Odas plan is.
And how is it unnecessary? Kaido is too strong on his own
1) nami, usopp and chopper add nothing to beat kaido. they are irrelevant. we all know that.
2) excluding jinbei (10th member) just to fit the narrative of 9 shadows doesnt make any sense. the 9 shadows might not even refer to 9 people, so trying to find 9 people to fit the puzzle is highly questionable.
3) this arc is not just about the SH, its about wano and the samauri. Oda has made it very clear with the amount of time he spent on depicting each of the 9 scabbards and even Oden's backstory. Having nami, usopp, choppers as 3 shadows are an insult to Toki's prophecy and to the 9 scabbard's resolution.