The Nikon D3x was shown in the Nikon Pro magazine,and scans of the magazine can be found here and here. As you can see below, it shares many features with D3 but the main difference is in resolution as expected.

Nikon D3x Main Features:

• 24.5-Megapixel 35.9x24mm Full Frame sensor
• 16-bit EXPEED engine
• 5fps at full-resolution
• 7fps at DX crop mode (10-Megapixe
• DX mode captures 10-megapixels
• Dual Compact Flash slots (at 35MB/s)
• MultiCAM 3500FX autofocus w/51 points
• ISO 100-1600 (expandable to ISO 50-6400)
• 3" LCD (922000 dots, 170 degrees)
• Live View
• Battery EN-EL4a (like D3)
• Weather-Resistant Magnesium Body
• 12ms startup
• 41ms shutter release lag

---