There bringing vw bus back! I thought it was just a rumor.
As for the new 500 this is what I'd do:
1. Extend the wheelbase by 10" (give the rear seat more legroom)
2. Extend the rear overhang by 10" (give the rear hatch more room)
3. Overall car is 20" longer which makes it the length of a Fit or CRZ.
4. Change the horrible rear suspension geometry and spring placement. Use the same design rear axle but stand up the rear shocks, put coilovers on it and flip them upside down. This gives you the most room and not making the car a compromise. Plus, you don't have the spring in a separate area which causes those cheap rear axles to bend. FYI: The term coilover is a spring that is around the shock (i.e. like every McPherson strut. The aftermarket uses the word "coilover" to mean adjustable spring perches and some adjusters on your springs that are separate from the shock, thus wrong terminology. It's like calling a dog a cat. Both pretty much do the same thing but are not the same).
5. Change the front suspension and get rid of those 40 year old crash bolts. Get with the program and make the shock slip fit into the kingpin and use one single pinch bolt. Alignment is held way better and it's a more robust attachment. There's a reason why most other car companies went that way. It's a superior design.
6. Change the rear seat design where the lower cushions hinge on the front. Thus, you can fold them forward to the front seat. Then have the seatback hinge like it does but where you get a flat rear trunk space when everything is folded down. A flat, bigger storage area wins over many people and you need to teach the sales people how to operate it. Plus, the press will love you for it.
7. Put in a 6 speed double clutch transmission with paddleshift. Pretty much like what I have in my Alltrack. I can drive it like I'm a big fat lazy American or I can drive it like I'm a lean German enthusiast by either using the shifter or those paddleshifters (honestly, it's really nice). Add launch control also (trust me that's is an awesome thing to have).
8. Offer a 6 speed manual for the 3% that will scream for them and then the press will love you. Put autoblip on downshifts (like a Mini does). Then you'll feel like a real driver.
9. Three trim levels for the 500. All with a 1.4l DI, Turbo 130hp motor. For the Abarth, 200hp 1.8l DI Turbo motor. Then a top of the line that bumps the power to 220, 4 piston calipers, better seats and more doodads on the body.
10. Redesign the dash and actually offer a regular media center that is upgradeable (easy $$$ for dealers) and Apple Carplay/Android Car Play on every car. Forget the CD player, this is not 1999.