I don't get this. Is this post saying that they are continuing to split the 1D product line? I thought the 1DX was created to be the camera that could do it all, so wouldn't it make sense to just upgrade the 1DX?
Marketing 101. Maximize profits by segmenting the market.
High FPS market
High DR / high MP market
Perhaps even small sensor or high mm (long lens) market
If you have 1 product that it all, it will be a compromise or it will be very expensive.
Think of cars: Porsche 911 vs Ford F150. Very different vehicles which go after different segments of the market
It isn't even that, it is that one camera can't do it all. Back in the film days the 1VHS could, it suited pretty much every pro shooting 135 format. It had speed when you wanted it, it had resolution when you wanted it, and it had high iso or large DR when you wanted them. The tech has moved on to the stage where one digital camera can't cover the best of everything, sports and press shooters really don't want 30+MP, they want 12fps and super fast AF, many other pros do want 30+MP and don't give a fig for 12fps.
It seems to me the speed of processing is a bottleneck, you can choose high MP and lower fps, or the other way around. Most that prioritise fps don't prioritise MP, there is such a split in photographers needs that one camera just can't cover all the varied desires.