We had this discussion before. You've raised the point that both Canon and Sony have beat Nikon in bandwidth. That is true.
However, I believe we can only assume that this is one area where Nikon is "behind" - for whatever reason. And it is possible that Nikon has good reasons. Nikon may do something better than competing cameras that requires more thinking time. But I'm speculating...
Remember, I'm addressing the idea expressed here that Nikon can "simply" drop an existing 24mpx sensor in a D300 body and, voila!, we have an 8fps body. I think that is a huge leap of faith that assumes Nikon can do it. That idea assumes the bandwidth required is "simple" and you are now agreeing with me that a D4 with 20 mpx or more would have been a better camera and a better seller, yet they didn't do it. Since Nikon is behind on this spec, we can only assume they would have done it if they could of done it.
>> The success of the D800 seems to fly in the face of your argument.
No, it doesn't. I view the D800 as a "studio camera", not *primarily* intended for the action/sports/wildlife market. That does not mean that it can't or won't be used for that, just like I know D3x shooters that shoot wildlife with that "studio camera". They would like the D3x to do it all and shoot 8fps but they are willing to make that compromise in order to use a camera not specifically designed for their application. You are doing the same with your sports shooting- you've talked at length about the carefully considered compromise you are making with the reduced frame rate of the D800. You make it up in resolution .
The D400, on the other hand, would be, at its core, purely a sports/action/wildlife camera. It would not be a "studio camera" because FX undeniably does a better job at those tasks (which include landscape work). And it is the wildlife shooters that are leading the drum beat for the D400, not sports shooters or landscape shooters.
An FX sensor with the pixel density of the Nikon P310 (a $300 camera) would approach 500 mpx. In principle, the only thing stopping Nikon from making a 500 mpx FX camera (or a 225 mpx DX camera) is sensor yield. It was sensor yield that supposedly justified the price tag of the D3x. Now obviously a major advance in yield has been made, such that 36 mpx is relatively cheap.
As yields increase even further, sensors will get denser. That is a certainty because pixel counts are the primary seller of new updated cameras.
Bandwidth is an entirely different matter, and has it's own unique technological hurdles, with unrelated timelines of advancement. An advance in sensor yield is not necessarily coupled, at the same time, with an equivalent advance in bandwidth. Those diverging lines are why I think the market for 8fps in something like a D400 will have to adjust over the long haul. Short term, though, I think a D400 with less than 8 fps would be a marketing disaster and that is embodied in all the D400 related threads here. There are still too many people demanding that spec for Nikon to go backwards and they have never gone backwards on frame rate- yet.
You seem to be agreeing with me now yet disagreeing at the same time. You agree that the D4 is relatively pixel poor, based on your own statement above- not enough for you to upgrade. Nikon lost two sales just from you. Yet you are also suggesting bandwidth is not the issue (with the D400) and that is contradictory. So I'm not sure exactly where you are coming from on this.