The 27th will be a reveal trailer and it will show Ness and Lucas and then Isaac comes along to fight along side them. Why 27th? 20th Anniversary of Earthbound (Mother) and what better way to introduce the veterans than to include Isaac along with them. Plus, the 27th is on a Wednesday. There is some significance to it. If this actually happens....
Remember, Ness and Lucas are never mentioned either (plus other characters too. Not just Isaac). No one can figure out who is in or out. Many say its Lucas that is cut or Ness is cut, or both or neither. Honestly, this just reminds me of the Brawl hype. Almost everyone thought Ness was being replaced by Lucas, but lo and behold, Sakurai comes in and proves them wrong. And I'm sure he will do it again. I bet that Sakurai knows about the leaks and is actually taking advantage of these to create more hype and surprise us completely with something we never expect like always.
I can't wait for that day when we can say, "Remember that [certain leak] that made everyone crazy? Hahaha! Fun times."
Here's a cool thought, you know how the Mii Fighters and Palutena will have customizable moves? Well, Isaac would be the PERFECT candidate for that section. Think about it. How cool would that be. He wouldn't have to be just Venus based. You could have him be anything. Even an assassin class. Hehehe. That would be the smartest move for Isaac, Ever.
Also, imagine if Djinn were an item or AT that grant you certain element abilities when they are attached to you. Like if you have a Venus Djinn, your attacks will be earth based, Mars Djinn would be fire based, etc. That there would be awesome!