Amateur Photographer is not big on reporting rumors, but today they did just that: the Sony α700 replacement is rumored to have a new APS-C sensor with high ISO "up into the hundreds of thousands" and resolution of 25MP. The potential release is expected to be around September at PMA 2011 (now called CliQ 2011).
This upcoming sensor from Sony could be the base for the D300s replacement (D400?), unless Nikon really is designing and producing their own sensors now. Since the replacement of the α700 will be a direct competitor of the D300s successor, it will be interesting to see who will make the announcement first (my guess is Sony).
There are even some early rumors floating around that the D400 could go back to the PRO body design of the Nikon D2xs (pictured below) - that would be a way of "upping" the D7000 which currently has better specs than the PRO D300s model.
If Nikon really goes with a new full-body style for the D400, this will also ensure Sony that they will not have a direct competitor for their α700 replacement.