So I had a thought on why perhaps we are waiting till October 5th for the Reveal
So the thought is maybe that the Reveal trailer for CP11 is tied to whatever the Bonus Piece of content is. This would especially be true if the Bonus piece of content happened to be something that's like a New type of Story mode, or Expansion on the Story mode already in the game, as Hero and Sephiroth's Trailer show, they have incorporated story elements into the trailer
With that being said, I did have a theory. It may be on crack, but it could be Possible
So I remember this rumor from back then
Nintendo wasn't buying what Disney was Selling - Super Smash Bros. Ultimate (gamespot.com)
So Pretty much the gist is that Nintendo wanted Sora, but Disney wanted not only Sora, but Also Mickey, with a bunch of stages, Music, etc, which would cost 2/3rd of the Fighter Pass (so $20), and that Nintendo turned it down
But with the Bonus slot thing being available, I have a theory about CP11, and also the Bonus Content
Sora is CP11, With Mickey and other pieces of Content being extra DLC
So Pretty much the gist is that Nintendo and Disney managed to figure out a Compromise to appeal to both sides, so here would be the deal
Sora will be CP11, and will come with the usual Fighter Pass Content: a Stage, Music, and Spirits.
Mickey, along with More stages, More Music, and perhaps even more Spirits will be the Bonus Content.
This would explain certain things
-Why this Content is Bonus in the First place, and only tied to FP2 (as the Listing suggests). Because the Bonus content is tied to Specific Fighter in FP2 (in this case Sora)
-Why not only a Character like Sora is being saved for last, but also why this Bonus Content would only be revealed just now. Developing More Content than usual (with the extra Stages, Extra Character in Mickey, etc) would take some serious time, and put Sora at last
-Why CP11 will be revealed separately in a Presentation, and how this Bonus Content will fit into the Presentation. Because If you are gonna separate the Kingdom Hearts content that's featured in the trailer, you got to explain how Sora is CP11, but Mickey is the Bonus Content. You don't want people to be confused on what exactly they are getting. And since both CP11 and the Bonus Content is from the same Series, they both fit into each other into one presentation
In terms of the Pricing, if this is to be true, This Bonus content will be free for People that purchased FP2, as the Fighter Pass Sales will cover the costs of the not only all the FP2 fighters, but the Mickey Extra content it comes with
Otherwise, if you don't purchase FP2, Sora Challenger will be the usual $5.99, while the Mickey Portion will be an extra $5-$15 on top of all of that.
And if they were telling the truth, this would also explain why people like Alpharad and Maximillian know who the character is way in advance (in that Nintendo probably flew them out to let them see the trailer early and get reactions). According the Max, this Final Character is Crazy, and Having not only Sora, but also Mickey would be one of the biggest announcements in Smash History, if not the Biggest.
But if that's not the case, than My guess would be some type of Substantial New Mode. Something like Smash Run which may even feature enemies from the DLC Franchises, or something like New Boss Rush that includes New Bosses to the game, or something along those lines. Something that's big enough and would take good amount of Development that they would charge premium for, but are also willing to offer to people that have bought the DLC