I'd say more than roumors. The recent firmware update for the D3 had some files embedded for D3X and 24 Megapixel resolution settings. I'd say that's a pretty good roumor perpetuator.
With the Olympic games coming up, can't you imagine that the games would be a perfect time to introduce a new body and announce that certain photographers will be using it at the games? Of course, one wonders about that because the D3 would be a better sports camera for such purposes, but it's fun to guess.
As for the rest of the specs...only time will tell, but I strongly suspect that given a high megapixel count the camera will behave much more like a high megapixel count, FX sensor sized, D300... I wouldn't expect the high ISO ability of the D3 to carry over to the D3x, nor would I expect the same high speed frame rates.
I'd also expect that the D3x, if announced at 24 Megapixels to be priced somewhere around $7,999.00 USD. I'd also expect a price drop for the D3 by about $500 when the new body is announced....at which time I'll probably pick another one up.
Song... remember there is a market for those that shoot medium format and there is certainly a market for higher resolution images. There are those that shoot images that are used for posters, billboards, and a whole lot of other larger print sizes. More resolution means more options for cropping and remember nothing is a standard size anymore. 35mm frame size? 5:4, DX format... What is 8x10? What is 11x14? Is that standard? Hmm... what about 13x19?
Julio