When Roger found Joy Boy’s treasure, he and the crew reacted with hearty laughter. Roger wished that he had lived in the same era as Joy Boy, saying that his story was a funny one.
What if he was saying he wished he was born in Joy Boy’s era, due to Poseidon being alive in that specific time? I am thinking this is a good hint into the theory of “One Piece” being the destruction of the Red Line and the creation of one giant sea instead of it being separated.
At Laugh Tale Roger discovered the truths about the Void Century, the meaning of D., and the Ancient Weapons, which are all essential for the destruction of the Red Line and the World Government. Roger can theoretically access all but Poseidon, which would not be born until long after he is dead.
When Roger found Joy Boy’s treasure, he and the crew reacted with hearty laughter. What if Roger laughs because Joy Boy was also in a situation where he could not access all Ancient Weapons? Roger is frequently seen with an egg on his ship. What if that is Uranus, and Joy Boy could not access it due to the exact same reason Roger does not have access to Poseidon?
That is, whatever is inside the egg did not or would not hatch before the Ancient Kingdom lost the war? And thus Roger laughs because they are both essentially screwed by the same exact circumstances centuries apart?
But then if the egg would not hatch in time him being born in Joy Boy’s era would not change things, so perhaps it was slightly different but similar circumstances with one of the ancient weapons, or Joy Boy lacked some sort of knowledge that Roger did not, etc..