This is an interesting idea, but I think it loses out due to it's complexity. I've seen a version of this--I think in Popular Mechanics in the 80s.

Your proposal is even more complex though, because it seems you're proposing that both the forward-2-seat portion and the attachable portion have power-trains.

The one in Popular Mechanics had a 4-wheel small car with the engine up-front and front drive, that would hook to a two-wheeled articulated cabin that attached to it and could share the same interior space, so you could talk to the back-seat people. You're sort-of forced with this idea to combine the interior spaces when the vehicles are joined, otherwise, it's no more effective than pulling a people-trailer on weekends when your commuter car has to take the family to church.

Anyway, this probably requires you to have six wheels (or at least five), complex braking issues, lighting and HVAC and air sealing and for that matter crash-worthyness issues. Then you still have the PITA factor of hooking it up all the time. I regularly pull trailers with my truck, so I know that backing in just-right and hooking things up isn't a task that I want to do every day.

As for "SUV", I don't think you could solve the structural problem sufficiently for off-road use. It would be more like a people-hauler.

Instead, we have a minivan for weekends and I commute in a little cheap car. I think it works out nearly the same.