The phrase "rear cabin" refers to the back part of a vehicle where passengers sit. It usually describes the area of a car, airplane, or boat that is located behind the driver or pilot. Full definition
The key thing to me is the comment about lack of rear cabin space. (autocar.co.uk)
Using a smartphone app, the Odyssey driver can control the rear entertainment system, rear cabin heat and air conditioning, and send destinations to the navigation system. (autoweek.com)
This plays an even more important role — allowing extra light into the cabin, which in turn helps reinforce the effect of the new car's extra rear cabin space. (motoring.com.au)