I agree with just about everything you're saying in your post.
May I add MB-D12 (the D800 battery grip) compatibility to your list? Furthermore I'm assuming that the "D800 body/handling" for your projected D400 is at a minimum including pro-button layout (including dedicated AF-ON), built-in Speedlight w/Commander mode (a C-channel would be nice), proper weather sealing and a magnesium body.
Some trickle-down from the D4 would be nice: lighted buttons and an ethernet connection...
My guess: - There's quite a price gap between the D7100 and D600... - Canon will certainly release the 7D MkII... - Nikon has been refreshing the DX body line from the bottom up (D3200, D5200, D7100) So what's next? A D400!