ok, I think the conclusion is the majority want to keep this feature, with the minority either not bothered about it or are not bothered to register the fact they don't care about it.
And to answer the question about why I think this may require more cpu and memory resources (not disk based, as I never said this), I'll give you an example.
To run two players, split screen on the same TV the game engine in theory will have to draw extra 3d objects for the backgrounds and track assets which will take extra memory/cpu resources. For example, if you have 10 3d assets for 1 player, lets says for the bridges, barriers, sign posts etc, for 2 players the engine will have to draw 20 assets, as both cars will never be at the same point in the 3d space with the same viewing angle on track. Therefore you will have to draw and render 10 3d assets for each half of the screen - they will just be drawn half size.
So to continue this example, the question is whether the single game mode only had 10 objects to draw or it had 20 objects, but they reduce this for 2 player mode to compensate, or they leave something in reserve in the single player mode, so they can process extra assets etc for 2 players.
It seems from prologue that they reduce the post processing effects and remove some of the extra features to compensate for having to process 2 input controls, 2 forcefeedback terrian mapping, and the overhead of having to draw more 3d objects on one TV.
So we will never know if they balance it out, so in the end the memory and cpu overhead is the same as a single player mode, just without the bells and whistles, or they have to leave something in reserve on the single player mode to cope with the additional overhead for 2 player mode.
I just hope they make the single player mode the best possible, and compromise the 2 player mode, rather than leaving something in reserve, as I will be playing single mode with AI or online far more than 2 player mode.