This is not the news of a confirmation, or a leak or anything like that. Super Smash Bros. Ultimate has not officially received Sora from Kingdom Hearts, but a fan has managed to sneak him into the roster through a mod, which has led to a video in which he gives the appearance of being part of the title without any problem.
Here is the video from the mastaklo channel:
As we say, it is nothing more than a “home” job, but they have placed it very realistically. Also, he has the look of the character in Kingdom Hearts 3, and of course he comes with his keyblade. It wouldn’t be crazy to think of Sora in Smash Bros., given that Square Enix has had dealings with Nintendo reaching the level that Sephirot and Cloud are part of the roster, as well as the little collectible skins.
But it is that they have even added lines of dialogue that they have taken from the third game of the Kingdom Hearts saga, instead of the phrases that the character says that he impersonates through the mod, which is none other than Shulk (from Xenoblade Chronicles).