John, the D3X has a 24.5-megapixel FX-format sensor and sells for about $6,699.00 today. The D800 has a 36.3-megapixel FX-format sensor and sells for $2,796.95. That's a heck of a difference. While there are differences in the two DSLR's feature sets, some significant, they are competing with each other. Of the pros I know, who are seeking a high pixel count FX sensor based camera, for portrait and other work, for example, no one is thinking D3X. It's all D800. Personally I don't understand why Nikon didn't stop producing the D3X a while back.
I would suspect that Nikon is trying to reduce D3X stock and may finally be halting production, but I don't think that signals the D4X is coming soon. I think it's more that the D3X sales have been victimized by the D800.
According to Nikon Rumors, the D4X isn't coming out anytime soon. I'd add, if at all. I don't know anyone outside of Nikon management you believes they have a clear picture of Nikon's future strategy. I know I don't understand where they're headed at this time.