The problem with a narrower can is that the rotor is narrower as well and you lose torque. Where are you running into problems where 36mm is a problem?
A narrow can would accomodate a more narrow chassis layout. I could potentially have the motor can on the same side as the diff case, thus making the centre diff/motor section much more compact. Or it could even be possible to mabye mount the motor on the chassis and have the battery right beside it without having to push the battery even further off the chassis centerline.