You don't hold a press conference to just announce a single game, no matter how big it is. Something like this is more for a massive regime change or new system.
My money is honestly on a 3DS revision, not the insanity we are seeing "Rumored" but enough of a revision to change and fix the complaints with the Current 3DS and enough of a name change to make people realize it is not the same system as the DS.
This however is just my two cents.
The patience it takes to play FFXI and EQ is the patience it takes to kill yourself by bashing your head into a wall.
Has to be something big, bigger than any game would ever be. It's hardware of some kind. 3DS Revision, new spinoff handheld like the DS was after the GBA, something to eventually replace the 3DS, who knows.
The announcement of a new species that will change the world. Pokemon was based off of a real live Pikachu Nintendo was hiding in an underground vault. Now they have bred the animal and will become an energy company, selling the creatures to power our world and appease the environmentalists. However, this may cause new debate with animal rights activists.
Later they will release the secret toilet pipe that ends in another dimesnion in which Mario was based off of.