Recently I was doing some research on the Volkswagen Beetle and was intrigued by the fact that it was built for 65 years using the same layout and only minor design changes during its long life. This is probably the benchmark, if we don't include the Morgan +4/+8 and derivates. The Ford T Model was built some 19 years. The Mercedes SL (R107) is probably the latest long runner with 18 years. Most cars today end up with a life span of roughly 3 to 8 years. Often there's one of more facelifts during the car's life.
So, would a car being produced for 18 years be thinkable today? It's a lot harder today than it was in the past. Safety regulation for example are influencing the shape of the car. Design has become much more important as a differentiatior than technology. Marketing and PR is way more important today and therefore drives car design and model strategy. So with quite a high probability we will not see again cars being produced for 10 and more years any more. Which is bad for collectors (parts availability) and bad for resale value (model changes increase depreciation), but good for the motor journalists and the car manufacturers I assume.