Good LORD, this chapter… O_O
The discussion between Big Mom and Kaidou is very interesting for a number of reasons, as a number of people (particularly in the spoiler thread) have pointed out. It gives them a more complex, more natural dynamic than simply opposing "gang leaders" who don't have anything to do with one another unless one encroaches upon the other's turf. Even though they're ostensibly "equals" as rival Yonkou, the fact that Big Mom seems to have something that she can hold over Kaidou to try and nudge him in one direction or another makes her even more dangerous than previously known (and the Totland arc went a long way towards hammering home her threat level in my mind). Obviously, that doesn't mean that Kaidou will follow her orders on the matter of who gets to kill the Strawhats, but the implication that she might become involved in Wano, and possibly even show up in person, raises what was already going to be a massive arc to another level.
It also makes perfect sense why the Marines would be freaking out over the intercepted communications - even though it was in the background, they went to extensive lengths to try to keep Shanks and Whitebeard from coming into contact back in the day. The prospect of two Yonkou teaming up even temporarily, much less the chance that they might forge a long-term alliance, is a threat the Marines can't ignore. While Sakazuki seems hesitant to get the Marines involved, that seems more to do with the fact that Wano is not a member nation of the World Government (and thus might see it as the all out invasion of a foreign power) and they don't have a good measure of the power of Wano's military forces. The last thing they need is to have the Marines caught between Kaidou, Big Mom, and the forces of Wano simultaneously. Even so, Borsalino seemed curiously eager to go and, with both Luffy and Law making moves toward Wano, I have a hard time seeing Isshou simply sitting it out - and if either of them decide to head in that direction, I wouldn't be surprised if Smoker and Tashigi tagged along as well. I wouldn't rule out a significant Marine force making an appearance quite yet, regardless of Sakazuki's reluctance.
Add Big Mom and the Marines to what we already have on deck…yeesh... Wano is going to be absolutely massive. O_O
And though I actually completely forgot who they were at first (been living under a rock for the past few years trying to finish up my bachelor's degree), it's rather nice to see Momousagi and Chaton be canonized…
The idea of Pangaea Castle's "Empty Throne" is fascinating to me as well… The fact that the twenty kings of old stipulated that it was to remain empty and that their descendants - for all their corruption, greed, cruelty, abuse of authority, etc. - have made it a point of pride to keep it so is rather revealing about the mindset that led them to found the World Government. That the weapons of the original twenty kings are planted in the floor in front of the throne as a guard implies that the throne itself predates the World Government and that in turn implies that it was meant for someone to sit upon. This leads me to wonder if the World Government was originally intended to fulfill something akin to a "Steward of Gondor" type of role, governing in the absence of the rightful "king" until he or his heir returns to claim their birthright - or perhaps more accurately, that the twenty kings feared concentrating power over the entire world into the hands of a single individual and set about to ensure it did not happen by either forcing them and their family into hiding or flat out murder (possibly both). Apart from the whole "and now we elevate ourselves to godhood" aspect, the general structure of the World Government seems to be very federal in nature, and even among the Celestial Dragons, their leadership is not that of a king but of a council of elders - and one that can't even keep their kinsmen in line, if the mobilization of CP-0 on Doflamingo's behalf was done behind their back as Sakazuki suggested. Consolidation of power, ironically enough, seems to be something the World Government was intended to prevent, more than enable. And, as one would expect from someone as ignorant of the world as he, Sterry seems completely oblivious to all of this.
Speaking of ignorant and oblivious: Saint Charlos. I'd been suspecting that he might make a move on Shirahoshi, so I'm not especially surprised to see that being government-recognized royalty doesn't mean jack to a moronic, entitled "god" such as him. It's nice to see that her new acquaintances weren't about to simply give up when a Celestial Dragon tried to claim her. Rebecca had to be restrained, Sai and Leo (as expected of "secret" members of the Strawhat Grand Fleet) ultimately tried using force, and Vivi marched straight up to tell off both Charlos and Rob Lucci to their faces - and when Neptune was about to go to town, she didn't try to stop him so much as convince him that Charlos isn't representative of the people of the surface and to not to give up on Otohime's dream of migration because of him.
Which brings us to: Saint Mjosgard. Not going to lie, seeing him whack Charlos upside the head with a mace was damn satisfying. Wasn't specifically expecting him to make a return, but it's nice to see Otohime's efforts paid off in more ways than just a letter. Also nice to see further evidence that the Donquixote bloodline may be more in line with Homing and Rocinante than it is with Doflamingo.
And last but not least, Shanks meeting with the Gorousei. This brings up all kinds of questions, from "Why in the world would they let a Yonkou into Mary Geoise?" (though to be honest, could they actually stop him?) to "What is it about him that makes so many high-level people willing to hear him out?". Honestly, it amazes me sometimes that, even after ~20 years, we still have barely any idea what Shanks is really all about…
In summery, this chapter was fantastic! I don't know what they're feeding Oda over there, but seriously, keep it up!