I can’t see this fight happen. It’s not beyond the realm of possibility but there’s no hype revolving around Smoothie whatsoever. Oda usually takes some time to develop an important opponent and create big expectations. Only her title speaks for her but her potrayal is poor and she’s unimportant in the story. King, Queen and Jack are given way more focus and their portrayal is better so I think they’re more likely to fight the strongest characters.
Honestly I have no idea what Oda has in store for BM’s crew.
Some people have had some cool ideas for them as a means to make the war a bit more varied. I personally like the idea of Sword coming to Wano. The fact that Koby and Hancock are enamored with/admire Luffy makes me think that
A) They will become friends
B) They will come to Wano together to help Drake, since Drake can easily report to Koby that Luffy needs help (he last told him he was imprisoned and the info can be relayed to Hancock)
Plus, Oda is apparently excited for something Hancock related (as well as Sabo and Vivi but I think that is TOTALLY separate). So for the BMP, it'd be cool if Coby, Drake, and Hancock (and whomever else is part of Sword and a powerful Marine) and fought on the good side.
Cause I can totally see:
Hancock vs. Smoothie/Campote
or
Koby vs. Daifuku/Snack/Oven
in some regards. Not to mention I could possibly see a few minks and/or Carrot take on Perospero.
Basically I think the BMP's will get their due diligence during the War.