Nikon reps have explicitly said in two separate interviews that the D800 sits ALONGSIDE the D700 in the lineup. This would make it sound as if it's not the replacement. They even said it at the revealing press release. So, I don't see why everyone, including the review sites, are saying that it's certain the D800 is the D700s replacement.
As for the next camera announcement, I'm going to say there's a 90% chance it's a DX D400, 35% chance its an FX D400, 10% chance it's a D700 replacement with D3s specs and sensor (though how I wish it were true!), and a 0% chance it's the D7100. That will be for August. I would say Nikon is going to announce the D400 in the spring, and the D7100 and D3200 in the fall. This will give them 5 new bodies for this year.
Mark