Arcording to: http://help.adobe.com/en_US/aftereffects/cs/using/WS3878526689cb916558 66c1103906c6dea-7e94a.html#WSB9C92251-D2B9-49de-8B7E-EE981AD17522 you should be able to seperate XY dimentions for 2D point controls.
But if i add a point expression control (or any other control that have a 2D position slider) the Separate Dimensions button is grey.
How do i split them?
This is how it always has been. AE's property streams and the UI controls for them are hard-coded and the only reason it works for the position property is that it's actualyl one helluva an ugly hack that is equally hard-coded and not available within teh standard API functions.
I don't know what is so difficult about attaching one slider to X and one to Y? That's what you are trying to do. Five seconds and two click and drag's with the pickwhip. That will work with any array for any property that has more than one value like color, scale, orientation, or feature center.
The only time it may become difficult is when you are trying to use the Graph Editor to change the timing of different values without the aid of an expression controller.
The title of the Help section that you point to makes it rather clear that this is just for the Position property: "Separate dimensions of Position to animate components individually".
> I guess that is lack of competition...
It's more a lack of people requesting this. If you want to submit a feature request, you can do so here: