Doing research for a future theory I am going to put out, soon, I ran into an interesting clue I think Oda is leaving for a possible foreshadowing of future main story arcs.
During the Enel Cover Story Arc, we see him travel to the Moon and the background of 4 robots who reached there, previously, after the death of their creator or restorer, since he more than likely found them because they appear to be exactly as the ones on the moon, minus cosmetics differences (Side note: if anyone wants to do a theory on possibly how they could have been on “Earth” already, go for it, since I’m not gonna be). Regardless, though, upon closer inspection of their outerwear it becomes apparent, especially this “late” (lol) in the series, that their clothes actually represent the general story and arc sequence for the different main arcs.
At this picture, we see the order they are almost always lined up in (right-to-left: since it is Japanese, not English), unless some fight or event is occurring in the scene, which follows the main story arcs we see now. As shown, there appears to be 4 main arcs. So the timeline becomes, two main story arcs, Professor Tsukimi acts as the split for the 2-year time-skip, and two more main story arcs (Enel replaces Professor’s position, on the moon, so Oda was intentional about this set up, and the timeline keeps). Note: there are a few times where the positions aren’t held, but the majority are definitely in this order, especially whenever they are lined up. Here are the instances, and Oda makes a point to keep them in this particular order, at the end, when he reveals the most about One Piece’s main story.
So, beginning with who Mr. Knight, above and on the far right, seems to be, is to correlate well with the Skypiea Arc. The Knight Armor, grill (although being on bottom, now), and weapon all match Gan Fall’s,
And the double circle is everywhere in art style of One Piece, but it is especially prevalent in the Skypiea arc, as well as on Bellamy’s shoulders (ch. 232),
which match up pretty well. Thus, symbolizing the Skypiea Arc, containing many clues of the main story, as well as setting up Enel, who ends up so kindly providing these juicy cover stories.
The next in line, with the combat helmet and gear, gun (not in this picture), and soldier wear matches the certainly matches with the Marineford Arc (the little dude is basically a marine), which was essentially everything after Skypiea, minus the detour for Moria, and ends at the time skip (represented by Enel, now).
So, this leads to the little guy right after Enel. Looks familiar, right? It’s a samurai! It’s Wano! It’s where we currently are! And with Oda saying we are roughly 80% done, and he would represent around 75%, and keep in mind these cover story chapters came out in April, 2007. Almost 12 YEARS AGO, so with the reworking he did at some point, he said we were 70% done one year, then 60% a year after, then went back to 70%ish, this seems about right, leaving another main story arc after the Wano Arc. Therefore, it begs the question what does this last guy represent, and it seems Oda tried to be a little sly, on this one. He put the clue right next to the answer, except the answer he gave in the previous chapter. Let me explain.
In the last cover for the Enel Front Story Arc, on Ch. 474, we get the image for this guy, above. This is BY FAR the best view we get of the clue he has on the side of his hat, for any of the cover story pictures (Oda did a great job of only ever barely showing it, another reason I believe this theory holds up, and he decided to through us a bit of a bone, by giving us more on the last week). Looking at the symbol, assuming it is symmetrical, it appears to be an image close to something like this.
Well, where does something like this appear, you might ask. How about in the chapter immediately preceding this one.
That’s right! In chapter 473, we see Oda give us the only clear picture of what I can only presume is an earring, hanging off of Enel’s ear. So, based off the previous three robot’s clothes giving us the general plot, the last mainline story arc will contain Enel, presumably the robots (who are now is loyal subjects), the marines again (based off of military clothes matching the other robots military clothes), and then this is where it gets tricky, the black hat. What it represents I am not entirely sure. It looks close to a winter hat, and along with the gloves may indicate a person, or what I am honestly more hoping for someplace cold…Space maybe? Could also just be some place high up, or cold, but at least we will eventually (hopefully) know!
To wrap it up, obviously, this is a very generalized version of the main story arc, but I think Oda wanted to drop some hints in somewhere, and where else would be good, except where he also hinted at the origins of the Skypieans, and made the first point in the story he made it apparent just how grand of a vision he had in store for One Piece. So, there could be smaller arcs, as we had many other arcs pre-timeskip, inbetween the Wano and Final Main Story Arcs.
*Theory by RUgly Slinks