Aside from Craig's observation that if you release two cameras, one will not be a 5D Mark III, I also agree that the collapsing of the 1D / 1Ds lines into one doesn't mean that there won't be a high megapixel camera for studio use in a cheaper line, possibly with a smaller body. This is a conclusion I had come to earlier and I think that despite the apparent move by Canon into the "let's push small pixels" camp, we've only seen it for one camera.
I think this may be a good move on Canon's part. While many people will look askance at any 1D camera that has fewer megapixels than a 5D series body, the call for 1D series bodies with high megapixel counts (above 18) seems to be somewhat less than many expected, especially since there isn't really much of a gap between 18 and 21 (which is about where the 1Ds Mark III sits). The sort of situations the 1D X seems best suited for - sports and photojournalism - don't require more than 18 megapixels, really; at least not for most photographers. There's enough other features in the 1D X to differentiate it from other camera lines - and hopefully the 61-point AF sensor means that we can expect better AF sensors to start appearing in other lines, as well. And even if that weren't the case, if they could point to IQ advantages in the 1D X over another full-frame camera with more megapixels (though I expect that sheer shooting speed will be the primary advantage), that's another area where the camera lines will be naturally differentiated.
Personally, I've felt that 20 megapixels is something of a psychological hurdle, somewhat like 100 of an item seems like more than 99 of an item.