It is totally obvious that massive confusion exists amongst both drivers and controllers.
ATC never in my experience ask an aircraft to maintain a track. They either instruct you to proceed to a waypoint, follow a published procedure or fly a heading!
Whether or not it is covered by NATS/ICAO/PANSOPS, commonly all over the world SIDs are amended by the instruction 'maintain runway heading to XXXX' then etc.
This does not seem to be ambiguous at all. HEADING is HEADING.
I have sat on the end of a runway on many occasions with a strong crosswind and watched alternate aircraft drifting downwind and the next aircraft maintaining runway centreline TRACK.
Finally, while FMS equipped aircraft can maintain track simply, what about all the other lesser equipped mortals on non instrument runways who have no method of maintaining the extended centreline track.