Personally, I would put it in the comments rather than an actual page in the chapter. I can't remember if there's a specific rule or whatnot regarding it within the chapter itself, but I think discussion of the chapter should be made in the comments. Including for the translators/group lol. After all, that's where everyone else is gonna respond to it anyway.
And I would also put the spoiler tag on it in the comment section, but more as a "long post" kind of thing if you're gonna go into a whole thesis on it. Would also state in the comment before the spoiler tag that it is indeed just a theory. But that way if it did end up coming true, it would already be appropriately hidden from anyone stumbling upon it in the future.
That's more just a courtesy thing though than a rule. People speculate in the comments all the time and end up being right, it's only really a "spoiler" if you have actual confirmed information that hasn't been appropriately revealed yet.
