Guys
I have a theory
And I think it makes a lot of sense
Okay, so, Dark Beast Ganon. Not many people like him. He was a terrible boss. But, it makes sense with the story of the game, right? Ganon lost control and transformed into a big glowy pig and if you die to him the world will end. But! What if I told you it would make more sense to have the Hero face a more personal foe when he reaches the final battle. To make this make sense, we have to look at the dragons of Hyrule. One for each part of the Triforce. Dinraal, power. Farosh, courage. Naydra, wisdom. Two of these dragons fly free when the Hero awakens from his 100 year slumber, but one lies infected upon Mount Lanayru. Dinraal and Farosh soar openly, symbolising the fact that Power and Courage are alive and breathing. Link and Ganon are in Hyrule. But what about Naydra? Naydra is corrupted by Ganon's malice. Naydra represents Wisdom, right? Who holds the Triforce of Wisdom? Zelda holds the Wisdom, which Naydra is the servant of. This COULD represent two things, either Zelda is weakening (That's literally the plot of the entire game) or that the Royal Bloodline is weakening and that each Princess Zelda has a little less of the Blood of the Goddess. This could mean that Ganon could latch on to the Princess because there would be less Divine Power to stop him. What if Ganon latched on to Zelda 100 years ago when she sealed herself inside of him and corrupted her with his dark influence? The corruption of Wisdom shows on Naydra, the servant of the Spring of Wisdom and that's why she's the only dragon whose been corrupted. Why? Because Princess Zelda has been taken over by Malice. What if... At he climax of Breath of the Wild... In the centre of Hyrule Field... You beat Ganon in the Astral Observatory, and you come face to face with Zelda. But she's not the same Princess you saw in the memories. What if at the end of BotW, instead of fighting Dark Beast Ganon, it was a duel against Princess Zelda herself. This has happened before. Take my favourite Zelda game ever, Twilight Princess. At the climax of that adventure, you journey through the labyrinth of Hyrule Castle only to meet the mastermind of the entire story, Ganondorf. He delivers some boring dialogue, before possessing the limp, lifeless body of Princess Zelda. Also, don't worry she's not dead. Then you fight Puppet Zelda.
There's nobody telling me this couldn't happen in BotW because it also happened in Spirit Tracks. In that train related journey, Chancellor Cole separates Zelda's soul from her body to resurrect the Demon King Malladus, who needed a suitably divine body to inhabit. The result? The most cursed looking thing I've ever seen.
And that concludes my theory!
...Sorry that was so long...