I was rereading the Zou arc when I noticed something peculiar about Momonosuke.
We all know that in the last chapter (chapter 820), Momonosuke made a unbelievable claim that he met Roger. But we failed to notice that Momonosuke previously made a claim which is similarly absurd. Look at this conversation here:
Momonosuke is essentially saying that Inu and Neko were close before. Now, the content of the statement is not the weird part here, but the fact that it came from Momo, an 8 year old boy! How could he know that? The way Momo said those lines, it’s as if he is claiming that he met Inu and Neko before, which we all know is impossible. This impossibility was emphasized in Chapter 819 when it was mentioned that Inu and Neko started hating each other when they returned to Zou which happened before Carrot was born (who is obviously much older than Momo).
Now, what could his possibly mean? We all know Oda won’t put these things for nothing. It would also appear that Momo is not lying in those statements.
Then, I was able to come up with a conclusion when I started relating these statements with the ability of the main family of Kouzuki to read and write the poneglyphs (I say the “main” family of the Kouzuki because it would seem that only the heir of the Daimyo is taught this ability).
I believe that Oden was actually able to transfer his ability to Momo. This ability is not a simple ability to read the poneglyphs. I believe this is an ability wherein the consciousness or memories of the transferor (which in this case is Oden) is passed/transferred to that of the transferree/recipient (Momo). This is the reason why Momo knows Inu and Neko, as well as Roger. However, his ability is not yet polished, that is why he can’t read the poneglyphs.
Lastly, I believe the Shogun of Wano has an idea of this ability and how it can be transferred. That is why they were not afraid to kill Oden despite the fact that, aside from Robin, he is the only person who can read the poneglyphs, because they thought they would capture Momo anyway. Hence, the reason why Kaidou is after Kin’emon et al. is not because they thought that Oden told them the secret of the world, but because they want to use Momo’s ability to read those poneglyphs.
*Theory by Henry D. Mont
the face of Momo when he hugs Nami, a dirty old man face
the things that you listed do highlight that there is definetly a thing hidden. Oda would never let momo say that he met roger just because it´s funny. That´s his style to forshadow something essencial or something big but i don´t think that there is some kind of ability thats let´s you transport your conscioness into another person because that is just too unrealistic in my eyes, it sounds too much like “magic” and that doesn´t fit into the rules of the word of one piece. However i think that there is a big revilation with momo that will come and nearly knock us all out. ;P