I thought you would have included another post of mine in which I basically said the same thing. Sorry about that.
I just don't like it if people say I make their head hurt or anything. If someone does that to you during a conversation, that isn't that nice. I apologize for the misunderstanding regarding the crystall ball.
I spoke confidently because I do know roughly how many chapters there are per year, and how long certain elements in the story such as feauture fights or flashbacks, arc climaxes, etc, usually take. Even though the arcs vary in lenght, they always follow similar patterns, for example there usually is a flashback right before or during the climax, which usually features a Luffy feature fight. There many patterns that haven't really changed since the very first arcs.
Like I can't say how long exactly the plot will take, but I can say pretty confidently that it is fairly unlike for Luffy vs Blackbeard to take less than 10 chapters, for example.
If there are around 300 chapters left which is a rather generous assumption, and we just look at the very long list of things not properly concluded yet (Shanks, Blackbeard, Ex-Shishibukai, Bonney, Urouge, Admirals, Revos, Im, CDs, Smoker, Vegapunk, CP-0 and probably a lot more stuff), as well as think about certain things that are bound to happen such as a Luffy vs Blackbeard feature fight or a flashback around the Void Century, then it is rather unlikely that Oda does not use the opportunity present at Wano arc and conclude the plotlines of certain characters involved there. With Luffy defeating one or two Yonko soon, acquiring his third Road Poneglyph in the process, Kid loses his merit as a rival, especially because he is fairly likely to pass out at some point vs Kaido. That is quite likely because Luffy will have to be in the spotlight during the vs Kaido fight. That's another pattern of One Piece, it is always centered around Luffy.
That's why I think Kid will be concluded in Wano arc. After Wano arc, there will be no feat left that he could do that would put him on par with Luffy. We have a whole lot of other mysteries around Shanks, mainly the dialogue with the Gorosei and what that means for his status and what it was all about (quite likely Blackbeard).
Whitebeard and Oden were brothers, that was his identity in the crew instead of a son. Roger and Whitebeard
Ace motivations are revealed during the Marineford war. All he wanted was to have a place in this world.
I think he is more like the Gecko Moria of his generation, and I would compare the Supernova more to the Shishibukai that gathered at Roger's execution than the legendary generation itself. None of the Novas feats compares even slightly to the monstrous abilities of Roger's generation.
But one shouldn't compare One Piece characters linearly anyways. It's more like twister, and Oda shuffles a lot of stuff from history, pop culture, other fiction, etc. etc. around to create and support his stories. Via certain underlying themes, visuals or background references, it is possible to link a lot of characters together, and while I think some of it is important, a lot more is just for fun.
Because the Supernova are such a late and sudden addition to the story, I don't think they have that much importance for the overall plot. I mean, with the cover story, Bege seems pretty much concluded with a happy family life, and I think the same will happen with most other characters involved in each arc from now on.
Law's plotline for the battle will involve some shady stuff based on a plan he agreed on with a mysterious person. I don't really see him set up that much for fights.
Since the mysterious person was not revealed to be Denjiro, I think it is fairly likely that it was Drake, but we will see.