OK so first I'm going to assume that Pluton is a reference to Pluto since they are spelled simularly, and because one is referred as the midget planet and the other is the exact opposite in their world.
In 2015 a dark-red region was found by japanese researchers on Pluto, it had the shape of a whale. Zou also was realised in 2015, so there is a possibility that Oda referenced the discovery.
The poneglyph that the strawhats found on Pluton was RED, this is a cool coincidence, but what does the whale symbolize and why will Pluton destroy the RED line. Let's get to the meat and potatoes of this theory.
The first time we hear about Pluton is during Water 7, we also learn that Pluton was constructed in Water 7. Right after that we meet Funkfeed the first inanimated beeing that has "eaten" a devil fruit. After it "ate" the fruit, Funkfeed became an elephant-sword
I think that Oda is foreshadowing that before becoming an elephant Zunesha was an inanimated object. Foreshadowing all that while revealing Pluton, the antient weapon seems kinda fishy.
The first time we see a whale in the story is during the Alabasta saga, there we see Laboon. His souly purpose is to destroy the Red line, also during his flashback we learn that a promise has been broken a theme that may be related to Pluton during the void century flashback.
OK so Pluto(Zunesha) is a ship that will destroy the Red line and is somehow conected to a whale.... a whale and a ship.... a whale ship, I've seen that before.
Luffy will arrive at the battlefield with Pluton and shock the whole world just like Whitebeard. 😱😱😱