Nekumamushi's mission won't be significant and impactful enough to let him take this long if all he would come up with were 200 additional fodders. he's definitely bringing up some powerful allies.
It won't be anyone other than some WB Pirates, since they're the ones who he actually went to sea to find.
And of course it can be impactful. Scene where the alliance is overwhelmed, all seems lost, then Zunisha comes crashing into Onigashima with Neko and the rest of the Minks who all go moonlit super saiyan. If he has Marco or Izo or Jozu or Vista, all the better.
Oda will find a way to make them reach Wano whether with Jinbe's help or via other means for plot to progress, they have Luffy's vivre card. more importantly if the Strawhat Grandfleet won't show up for a massive war including two emperors like this when Luffy is in dire need of numbers, then when would they?
They're meant to grow and power and cause a great incident of historic proportions, so presumably then. Very hard to say them showing up and fighting fodder in the background- which is what they'd be doing on Wano, since it's the Strawhats, the Scabbards and the Worst Gen who'll be fighting the relevant enemies- fulfills that promise from Oda. Especially since their meant to "cause" this incident themselves, not play a tertiary role in a war thats been in the making years before most of them were born.
If anything it'll happen on Elbaf- we know Hajrudin's dream is to be the King, so he'll probably play a big part in that arc. If Oda ties that in to Barty burning Shanks flag and Hajrudin's history with Big Mom then there's plenty of room for the great incident to be caused there.
Informing the giants of Big Mom's presence on Wano could also work. apparently, Big Mom pursuing Luffy in Wano is something known (as mentioned by Teach reading the daily news) but Nekumamushi could further explain to them they have a plan and other allies to take on the Yonko. It won't only boost the alliance with powerful allies replacing the Whitebeard remnants, but also would solve the Mother Carmel mystery since giants are the only people who knew about what happened at Linlin's 6th birthday.
thus, saving us from another unneeded Big Mom showdown on Elbaf and sealing her plot forever.
Have to disagree. Think it throws a very unneeded addition to an already packed arc, that makes more sense to be saved for Elbaf where it will be a main part of the plot.
And Big Mom, whether as O-Lin or herself, is going to be on Elbaf. Her story is too tied to the place to be wrapped up in a totally different arc as a side piece to the main story of opening Wano's borders. She's not going out the story here.
I don't really see how they won't be considering Oda has already established the big mom pirates alliance with Kaidou as the new Rocks pirates the most unprecedented alliance as Sengoku dubbed it IIRC. Big Mom pirates failing to live up to the hype as antagonists will be anti-climatic asf imo. Something important to note, is that Big Mom is missing two of her sweet commanders which I think significantly lessens the hurdle for the alliance. Imagine if the alliance had to take down both Katakuri and Cracker in this arc ^^". So the alliance can do it, but they'd prolly be needing more allies which is almost guaranteed to come in the form of sword and we could potentially also see Hancock on Wano depending on how her encounter with Coby goes. I think Oda is setting up another Pirate + Marine alliance vs Rocks confrontation.
Also Wano seems to have major ties to OP so could be why Oda is making the hurdle for the antagonists so high.
The "alliance" between the two has always came with caveats for me. There's been a lot of mention of it being "tentative", with Sengoku pointing out that Kaido and Big Mom have had a "tempestuous rivalry" and that the Rocks in general despised each other and spent a load of their time infighting. I think it's a lot more likely that we'll see a betrayal here than the two actually working well together. I don't really think there is much hype for the BM Pirates as antagonists here- she's spent as much time on Chopper's side as she had on Kaido's, and her crew have had no effect on the arc whatsoever.
Hancock doesn't make any sense to show up here. She'd have to have the magic teleporting fruit that people seemed to think everyone possessed back on WCI when all these allies to defeat Big Mom were apparently going to show up. Sengoku, Sakazuki, Drake and Coby told us that SWORD and the Marines are too stretched with whatever happened at Reverie with Sabo and the Warlords to show up on Wano, especially since Wano isn't under their jurisdiction. It's CP-0 that are set up to play a role.
You've got to keep in mind that Kaido and Big Mom aren't the true inheritors of Rocks will. That's Blackbeard, who's literally going to be a bigger villain than both of them combined because, well, that's how story works. Escalating threat. So yeah, we might get a repeat of Gods Valley, but it'll be Blackbeard playing the role of Rocks, not these two.