The Mustang Mach E is inevitably a polarizing subject,as the idea of a Mustang being anything other than a two door coupe/convertible is apparently heresy in the minds of many. But things might well have been different from the get-go: this four door sedan concept shows that Ford was seriously considering a wider line of Mustangs, presumably to replace the Falcon altogether.
That would have made quite a lot of sense, as the Falcon was getting old by this time, and Ford was reluctant to invest in a new one. As it turns out, they never quite did, just cutting down the 1966 Fairlane a bit to make a Falcon. That didn’t go over all that well either.
We’ll never know how close Ford came to putting this into production, but it’s interesting to speculate on how things would have turned out if they had. I’ll speculate that this was something of a fall-back plan, in case the Mustang didn’t catch on, as a way to amortize some of its body tooling. Ford’s target was some 100k units per year; that’s not a lot in terms of amortizing a new body.