With the currently existing API it's not possible to swipe in any arbitrary direction, but only in a defined GREYDirection (left, right, up or down).
Swiping in any direction, for example from a given start point to a given end point, might also be needed to test some UI components.

I propose adding new public swipe actions, that take a start point and an end point and perform a swipe along these points.

The API for the actions might look like this:

grey_swipeFastFromStartToEndPoint(CGPoint startPoint, CGPoint endPoint);
grey_swipeSlowFromStartToEndPoint(CGPoint startPoint, CGPoint endPoint);

The implementation might be either a new GREYBaseAction subclass, or by extending GREYSwipeAction with this functionality.

This can be implemented similar to the existing GREYSwipeAction, by using

[GREYPathGestureUtils touchPathForDragGestureWithStartPoint: endPoint: cancelInertia:]

instead of