My insane wish:
WB and BB battled. BB's power to nullify DF is rendered useless because Whitebeard (and ALL Yonkous i hope) ate no fruits whatsoever and has another kind of power that's even more powerful than a black hole. King's Haki, Emperor's Haki, or whatever. I hope Whitebeard has some brutal ability, for example: destroy someone's specific ability permanently (In order for it to not to be too powerful, it should have limited number of use or else it'll be too much damage to WB's own body which can lead to death), such as swimming, fighting, thinking, their memory, or even the ability to use Devil Fruit they ate. Owning!
After the battle, Blackbeard lost his DF ability and also his memory (due to Whitebeard's ability, kekeke) and fled to start a fresh, new life. While Whitebeard was exhausted from all the fighting against a few Shichibukai at once. The other Yonkous were busy fighting the entire Marine and World Government over Pluton and Poseidon which had been resurrected. But Robin gained some knowledge from the Poneglyphs and apparently the knowledge is the only way to control both Ancient Weapons. So. Robin gained total control of the Ancient Weapon, became freakingly powerful and established a significant role in ending the war. But, in the ultimate battle, Pluton and Poseidon were destroyed effortlessly by a single entity, who / which is…read below.
My ultimate insane wish:
I wish One Piece is something alive, like an origin of all Devil Fruit, which has mind and will of its own. And it's taken a liking on Shanks because it reads the past about Shanks saving Luffy at the sea without care about his own body. So, it enters Shanks' body through the stump / hole which had been Shanks' arm, creating a new arm and a second soul inside of Shanks. It also gives Shanks new kind of ungodly power which surpasses all comprehension and disintegrate anything opposing him, any creatures and creations, spirits, machines, weapons, continents, powers, anything. Shanks became the ultimate final villain. Not exactly a villain, though, since he held his principles and his conscience was undisturbed. But let's say, he became someone Luffy must face in the manga's ultimate climax, because he now couldn't stand anyone other than him to become teh Pirate King, and Luffy was aiming for just that.
Finally the new Shanks told Luffy to return his hat, and battle him (One Piece's personification) for the title of Pirate King because Shanks also desires the title, and the battle will be filled with ambiguity between adoration and rivalry, between excitement and passion to be number one, between one's own dreams and true friendship, "This is my final gift to you. Luffy." or something like that.
I believe all of that will never happen, though.