The Project Coordinates origin can't be moved. This is not a problem unless you have more than one coordinate system that you need to work with on your project. When the project only needs one 0,0 point, you can locate Shared Coordinates to align with the coordinates in question (Revit is more cooperative in this regard than it was in the past).
Now: you need to know that Revit ignores the BASE command in AutoCAD and assumes that 0,0 is the origin. Here's the deal: import a 100' circle with a 150' line from 0,0 going straight up drawn in AutoCAD with center 0,0 with the origin-to-origin option into Revit. The center of the circle will give you the Project Coordinates origin for your Revit project. This origin cannot be moved or altered; it's just there. I get users to put this into all their office templates so they know where this is and can use it effectively.
Now draw a (exactly) 5280' circle around the Project Coordinates origin. If the insertion point of the DWG (remembering that Revit assumes 0,0 in Acad is the origin) is such so that the whole DWG fits inside this circle, you're good. Otherwise, you're manually moving DWGs into place. So Revit works fine, provided the DWGs fit inside this 2-mile-wide circle. Revit objects can be outside this circle without affecting the insertion of DWGs.
An upshot of this: if the Shared Coordinates origin and the Project Coordinates origins are more than 2 miles apart, importing by Shared Coordinates always fails -- it defaults to center-to-center. So if your DWG is a mile wide and 0,0 is in the middle of it, the Shared Coordinates origin must be less than 1.5 miles from the Project Coordinates origin for import by Shared Coordinates to work seamlessly.
Edit: See the post below for how to acquire coordinates from DWG files with large coordinate systems.