Journeyman wrote:

If you can mentally translate from keeping the needle centered to your
position along an airway, you can do it whether the needle represents a
VOR signal, localizer signal, or GPS. That's the basic IFR nav skill to
master.

Well, but maybe that's the real question? Is visualizing location in space
by interpreting a CDI needle indeed a basic IFR skill? It certainly was
when I did my instrument training, but is it still? Will it always be?
The moving map GPS gives so much more information. Right now, we're in a
transition stage where a well-stocked GA panel consists of a moving map GPS
backed up by a conventional nav/com. Maybe 10 years from now, the standard
will be two moving map GPS units (or something more exotic), and the CDI as
we know it today will be as obsolete as the ADF is quickly becomming?