Its funny how people get hung up on what a particular marque should be, when their impressions are based on decades-old marketing campaigns.
Ford worked on one or two four door Mustang proposals in the 1960s, along with a Kammback wagon. IIRC GM toyed with a wagon concept for the 1970s or '80s Firebird as well.
The manufacturers are free to take their nameplate in whatever direction they wish.