This was mooted a few years ago in C&D or R&T, & it has intrigued me ever since.
POD of your choice, up through about 1970 (let's say). I'm picturing this being an existing maker, with established brand status, rather than, say, Bricklin, who'd also have to build a dealer network & brand loyalty, which kills its chances. (I'm also thinking of a U.S. firm, but I won't rule out Britain; I just think it's harder in the U.S. market.)
A company decides to produce cars on a single platform, with a single wheelbase: coupe, sedan (2- & 4-door), hardtop?, wagon (2- & 4-door), delivery (solid-sided wagon, for those who've never seen one) (2- & 4-door), & pickcoupe (similar to El Camino or Ranchero). Various trim levels & equipment fits, so various price points.
The theory was based on the GM example. The G-body sold easily 500,000 a year from 1978 through about 1987 (including Montes, Regals, Grand Prixs, & Cutlasses). Add to that the number of Crown Vics & Marquis, & Dodges in the same size class, sales easily reach 1 million. A company that could capture even a fraction of that (say, as many as Buick, around 120000) could reasonably stay in business, no? It might be a bit of a niche player (*Packard? *Porsche?), but...
Could a company actually survive this way? If it was going to make it, would it have to offer more frequent major styling changes? Or much-better than average performance? If more major styling changes were needed (desired), could this company pioneer robotics or plastic body panels to enable it? Would it effectively have to be more reliant on technology on the factory floor, & in the design studio, to keep costs down?
Or is this just some magazine writer's ignorant speculation?