Regarding OP, at the very least the story has gone out of its way to proof it exists and to boot it is of crucial important to the story's metaplot so to speak. And not only because it is luffy's objective and finding it makes him pirate king (... for reasons) but also because it is intrinsically connected to the world government and the true history.
What is interesting here is that roger and his crewmates found this place however upon finding it they did not feel the need or at the very least did not find it appropriate to act on this. Well, either that or it turns out they are pirates and actually lied about getting to OP. I mean, in theory roger's crew made it to OP. That wasn't a handful of people, it was something like at least 20 and out of them there were a bunch whose strength would shake the world. roger was a monster, rayleigh could take an admiral in his old age... Shanks seems to have taken after roger in a way however buggy does not seem like the type to keep quiet. Can you imagine buggy being familiar with OP and keeping it quiet? Of course, it could also be the case that they are pirates, not heroes and acting on whatever they found on OP was simply not something they give two consecutive shits about and simply forgot about it.
Now, the only reason the idea that roger and co not caring about OP does not have too much ground is that roger in his dying moments basically sent every pirate in the world after OP. Which knowing what we know now seems more or less like a huge middle finger for the world government. Which is also, probably not by accident of course, what WB did. On his dying breath he told sengoku that the world government was afraid of OP and that someone that would carry the weight of centuries will find that treasure and shake the world. I am not sure if roger told WB what was in OP however depending on what WB actually did know we could make the case that just pissing of the WG would be motivation enough for them. I guess that based on this we can also make the case that roger thought he was not the man to shoulder the weight of centuries over his shoulders and thus didn't act on what he found there.
Also, going over this I got an idea. Normally we think of OP as an endgame thing. Basically that finding it will be just about the last thing that happens in the manga. Well, short of the strawhats getting to reverse mountain and climbing to complete their trip around the world. However knowing what we learned at mink country and hearing WB's words I get the impression that OP isn't the endgame but rather what triggers the endgame. WB spoke, almost prophetically, that once OP is found the world will be engulfed in a huge conflict. We have known for a while that the manga is headed for a yet bigger conflict than the WB great war. However based on this the trigger for the next conflict will definitely be OP being found.
One thing that I can't quite make sense of is how exactly luffy plays into this. Because while luffy cares about his friends, he is not quite the type to shoulder the weight of centuries. For this to play out this way luffy would have to specifically aim for the world governments final destruction. Which wouldn't make sense to me. Luffy didn't fight any of the people he fought because of their history or inherent evilness. He fought them because they screwed with him. He fought arlong over nami, crocodile over vivi, enel over sky island, lucci over robbin and so on. But if luffy was asked to bear the burden of centuries I can clearly see him telling whoever asked this to suck the fattest of rubbery dicks. Now. it is not impossible that luffy more or less ends up playing into this role however it would have to be because the world government screwed with him specifically and his friends. Not because of history and whatnot. In context it would make a fair bit more sense that dragon is the one to shoulder weight of history because he has made this his business. And that would be a perfectly reasonable endgame to be fair.
