The dream of having a reconfigurable car on the market is one that many designers, engineers, and backyard hobbyists have attempted.
In my beloved World Cars 1978, there's an entry for the Prima that says:
"On the chassis of the Ford Fiesta and in collaboration with the Ford Design Studio in Dearborn, Ghia has prepared this prototype, the most versatile of the ones built up to now and with the widest range of uses. The estate car illustrated above is one of the four different cars into which the Prima can be transformed in a few minutes"
That's just about all the information I've been able to find on the concept. I'm not sure where the concept was first shown, apart from the year: 1976. Around this time, a number of manufacturers were trying to introduce multi-functional vehicles, and everything from the Mitsubishi RVR Open Gear to the Škoda Felicia Fun and Nissan EXA, with only the fun and EXA entering production.
How do you give customers a vehicle that can do multiple things? Ghia relied on a system of different backs, as Nissan did, and besides having to swap bulky body panels (not to mention store them!), maybe customers could trade in old modules for a body style they need—like a truck before moving house.
The magazines would have enjoyed the inevitable Prima vs. Dodge Rampage vs. Subaru Brat comparison tests, and I'm sure kids would have taken to "stancing" the car as well.