To reply to your questions:
> The reference instrument for all aircraft flying today is still the magnetic compass.
Yes. However once airborne the compass will not read the same as the potential mag track column unless there is nil crosswind. I'm afraid I therefore don't understand the relevancy of this statement.
The relevence of this is that all in-flight bearings should be derived from the same datum and magnetic is the one used universally. The CDIs on your nav instruments whether they be traditional steam VOR indicators or GPS driven CDIs need to be set to the MAGNETIC Track you intend to follow. The offset wind derived magnetic heading is the heading you fly to achieve the selected Magnetic Track
> It is the magnetic track ... that is entered into ... built-in IFR GPS's.
This is pretty compelling. When would you enter an actual track (whether it's true or magnetic) rather than simply entering the waypoints?
You would normally enter waypoints but you might well enter a magnetic track to fly on the HSI page of your GPS. Certainly your GPS should display the Magnetic Track to the next waypoint which should agree with the Magnetic track you have dialled into your CDI instruments.
> All runway headings are in degrees magnetic as are all bearings derived from VORs.
Yes, but it is unclear how having SkyDemon output legs as magnetic bearings is relevant to runway headings. Could you explain how bearings derived from VORs relate to one's PLOG, unless you are actually tracking along a radial?
It's not just bearings derived from VORs and you don't need to be tracking a VOR radial - any course you set in a CDI instrument needs to be set as a Magnetic Track. A CDI type panel mounted GPS Indicator as well as a VOR indicator (which may be operating in RNAV mode with a pseudo-VOR displaced onto the waypoint) needs to be set up with the Mag Track to the waypoint so you need that information on the PLOG.
> All bearings on airfield plates are in degrees magnetic.
Agreed. However the PLOG shows enroute legs only; could you explain how the potential mag track column will be used to relate to the magnetic bearings shown on airfield plates?
It doesn't but that's hardly the point. The real thrust of my argument is that you need to stick to one datum - magnetic.
Hope this helps.