Actually the subject is getting more interesting.  My autopilot (TruTrak) uses gps as its primary data source.  As a result, in the GPS-S or Track Modes, under normal circumstances, it flies a track rather than a heading.  The other mode is coupled to a VOR or LOC, in which case, of course, it flies the selected radial.  TruTrak is working on a coupler to a HSI or DG that would permit it to fly a heading but has not completed it and does not anticipate that it will be widely used.

In its present configuration, the only way I can fly a heading on autopilot (as, for example, when I get a vector from ATC) is to select a track on the autopilot that I think will work and then keep adjusting it so as to maintain a heading as indicated on my HSI.

Here is what the people I have called have to say about the subject:

EAA:  Never heard of the issue and have no knowledge of any FAA plan to give track vectors
AOPA:  Ditto
FAA:  Do not give track vectors and have no plan to do so.
TruTrak:  Don't worry about it.  Unless you have a hellacious crosswind, the difference won't matter.

None of these answers is particularly satisfying.  It would be nice if the FAA had some interest in joining the rest of us in the 21st century.