@Robby:
Half the crew didn't know about Laboon until it became important on Thriller Bark. The old crew never told Chopper, Robin or Franky about that old adventure.
Luffy doesn't know ANYONE'S backstory.
Etc.
And even after Wano we still probably have 7 or 8 years left to go in the series. (1 year for Elbaf, 1 year for Raftel, 2 years for stuff we can't know about, 3+ years for final war.) It'll be a long long ammount of time… especially if they show up early in the likely 2 year arc Wano will be.
Besides, just because we the audience will have a cutoff point on adventures for the crew... will they just stop when the series ends or will they have a lifetime of adventures and parties afterwards? Just think of all the movie or anime filler adventures the characters are having that aren't in the manga... and consider OP will probably keep getting some sort of perpetual releases even after the series ends in another decade.
There are already going to be dozens of known characters (again, Luffy, Zoro, Nami, Usopp, Sanji, Chopper, Franky, Brook, Jinbe, Carrot, Law, Law's crew, Momo, Kinemon, Kajuro, Raizo, Inuarashi, Nekomamushi, Marco, Kaido, The Shogun, Sheepshead, Ginrummy, Scotch, Jack, the two other calamities, X Drake, Apoo, Hawkins, Kidd, and possibly Weevil/Moriah/Caesar) that we know of who will be getting most, if not all, of the screen time in Wano. Sure, there will be a handful of Wano-specific characters, but even if one of them were a possible candidate, the SHs already have half of the road poneglyghs and they've already faced an emperor.
The major conflicts can almost already be seen as well (Luffy vs Kaido, Neko/Inu vs Jack, Zoro vs The Shogun, and Law/Sanji/Jinbe/Marco vs two other calamities/Drake/Apoo, etc.), so they likely wouldn't even be a major player in the overall conflict. That's why I've stuck with Carrot. She's there, she's familiar, and she checks enough boxes. Introducing a brand new crew member will require a ton of panel time (even for a two year arc) and I just don't see that happening because 1) we have enough known characters that need the extra development and 2) they likely wouldn't even play a decisive role in the upcoming arc anyway.