Capacitive sensing for touch detection is usually cheaper and more durable because of no moving parts, but it's tough to get reliable on outdoor stuff with varying humidity, condensation, and static electricity. Troubleshooting it in the field is nearly impossible without replacing parts.
I prefer the reliability of the pushbutton.
I haven't looked at the wiring of the Kia in detail, but on my old Hyundai locks were switched by a single trigger wire. A circuit that taps the automatic sideview motor signal and triggers the unlock would cost a few dollars in parts, even if some signal conditioning were necessary ..