I'm pretty sure Xebec is dead, if he was alive and as powerful as we've been led to believe I see no reason why he would have been hiding all this time.
As for his role in the story it should be noted that according to the Vivre Card databook, Blackbeard's ship is called The Saber of Xebec and that's probably not a coincidence.
It's suggested in Punk Hazard that his ability can be blocked with haki. When he fights G-5 Smoker tells Tashigi not to attack him because her haki isn't strong enough. And when he fought Vergo, Doflamingo mocked him saying his powers aren't stong enough to cut through Vergo's haki.
Law was able to cut through Vergo but those lines imply that haki strong enough can block his powers and the emperors and stronger warlords would definitely have strong enough haki.
Oda's estimations of how much is left have always been very fluid so don't take the 5 years too seriously, a better indication of how much series is left is a couple months ago Shonen Jump announced that the next Saga is the last one, the current one has been going on for 5 years so the 5 years remaining comment may hold some weight.
The Wano arc has been split into acts with us on act 3 and apparently Kabuki theatre in Japan has 5 acts so maybe there's loads left of Wano but it honestly doesn't feel like we're only 3/5ths of the way through the arc, unless there's another big twist coming.
Most of the remaining story threads could all be linked together fairly easily. WG, IM, The True History, Poneglyphs, One Piece, Laugh Tale, Revolutionary army all those things can be easily linked. Rocks was defeated trying to kill a World Noble in a place called God Valley so that could link him into stuff regarding the WG that and Blackbeard named his ship after Rocks so there's a connection there to link him in as well.
As the others said the first instance of conquerors was when shanks saved Luffy, the first of observation was in probably in Skypia, Enel and his priests could use it and the first use of armaments was I think when Garp punched Luffy in the post Enies Lobby arc, the fact that characters commented that it hurt Luffy when it shouldn't have confirms that it did legitimately hurt him and wasn't just for comedic effect like with Nami.
There is some implication that it has an effect beyond just knocking weak people out. Like when Luffy and Doffy clashed, there's no chance either of them thought the other was weak enough to be knocked out so why did they use it.
We've never seen him use it but it's possible he has it dormant and could learn to use it. There's no point asking if it's proven that he doesn't have it because other than the character or Oda saying so you could use that argument for anyone. It's never been proven that Orochi or Spandam or Caribou don't have it.
I got the impression that that was Kaido's fighting style. He doesn't dodge attacks because he doesn't have to, it's not that Luffy was "able" to land hits it's that Kaido let him. The difference between them was so great that Kaido didn't even bother to avoid the attacks.
Since they've started up again they're releasing them roughly every 2 or 3 months which was the same release schedule as when they were first doing it which means if they continue until the end they probably wont catch up until One Piece has finished because they release them in 12 episode blocks and it's usually about 12 weeks between releases.
It was a failed one, the successful ones don't have the laughing side effect.
There's a Devil Fruit Encyclopaedia that contains the names, appearances and powers but it's very incomplete there are loads it doesn't have because it's reliant on people having giving the information of what their fruit looked like to the encyclopaedia.
The Dark Dark and Clear Clear fruits were both in the encyclopaedia but it's probably safe to assume tthat Kaku's and Califa's weren't.
At first I thought Kaido but Hawkins was helping them trap and expose Drake so if he thought Kaido only had a 1% of surviving he wouldn't have sided with his subordinates there.
Next 2 I'm thinking of Momonosuke or Luffy, whoever he was looking at he thought it important enough to not take part in the battle to check and them along with Kaido are the 3 most prominent men on the battlefield.
He was also really interested in checking Luffy's chances to survive after Marineford as well.
I'm not sure why being born on Amazon Lily would give Mihawk his weird eyes no one else from there has strange eyes. Also it's been mentioned that the women from Amazon Lily only ever give birth to girls which is why there are no men on the island.
There's never been anything to indicate that Shakuyaku is from Amazon Lily or that she's connected to Mihawk in any way. Obviously I haven't seen the whole theory but from what you've said this theory just sounds like a complete guess based off no evidence. There are also a lot of theories about characters being the children or siblings of other characters based off nothing other than them both being strong and this just sounds like one of them.
He did notice all those things. The series is quite clear on the fact that he predicted all those things before they happened. With the picture Katakuri was trying to hold Luffy down because he saw what Luffy was going to do but he was unable to stop him from stretching his arms and with the mirror-world he was yelling at Brulee to go back in the mirror because he foresaw what Luffy was going to grab them both and pull them through but Brulee wasn't fast enough to react and yelling at her distracted him enough for Luffy to grab him. For the spear, again it's made quite clear that predicting where Luffy would dodge to and then attacking him there was exactly how Katakuri was fighting. It's just that the physical difference between him and Luffy wasn't so great that he could 1-shot him even if he knew where he was dodging to.
What you've got to remember is that predicting what someone's going to do doesn't necessarily mean that he could stop them from doing it. That was the whole strategy in Skypia, most of the villains of Skypia could predict the future the same has him but they all got defeated because they couldn't stop the attacks even though they saw them coming.
The official release for chapters is on Sunday's and the wiki doesn't go off the unofficial releases, so even though everyone's already read it none of the pages that will be affected by the chapter can get updated until the official release is out.
We already know what the message was, this chapter revealed it. It's "I might be late but I'll be there - Marco"
It was just Marco reassuring Luffy that he was on his way to help.
It covers part of chapter 934 but not all of it so start with that one.
You know what while looking this up I just came across this list on the wiki of all names in One Piece with spelling variations, what's official and where they came from.
Usually we have to wait until there's an official spelling given in the manga for the things that are debated, it's how we discovered how to spell Oars. Jinbe is spelled that way on his wanted poster so that's the correct spelling.
As Inari47 said Reverie seems like it should be correct because that's an actual word but it appears in the manga as Levely so that's how it's spelled, the same with Mariejois officially being Mary Geoise.
Raftel has been confirmed recently as Laugh Tale though I think that's a retcon on Oda's part because if you listen to the Japanese VA's that is definitely not what they're saying even taking Japanese pronunciations and accents into account.
Then I'm not sure, there's been no confirmation of anyone she's used her fruit on what we saw of her during the Levely arc suggests that she's is going to have an interesting backstory so maybe we'll get more details or see more people she's used her fruit on then.
Is it just by Bonney's fruit specifically or are you asking about characters that are just older than they look because if that's the case then Shakky comes to mind, she's over 60.
^Yea but he removes peoples hearts without killing them.