If you really want to get fancy, between the wiring for the mirrors, locks, windows, mirror heaters, perimeter lights, etc, there is enough current capacity and redundant wires to create a CAN network to control door-mounted options.
From a DIY perspective, 3x arduino modules with CAN shields - one in each door and one master module mounted centrally - would allow you to send commands to the doors instead of sending direct signals. Never pull a wire or touch the harness again. With sourced matching connectors it could be plug & play.
You would connect door "features" directly to the module, be they perimeter lights, mirror turn signals, mirror control, heated mirror circuits.
Change a pair of existing wires to become the CAN bus wires, and hook the modules to a switched 12v source.
With a little programming you could control any arbitrary number of devices connected to the doors.
Add a touch screen or bluetooth control to the master module.