Is it possible to accept analog input, digital input and provide digital output and analog out on a single MCU Pin?
Accept a input switched to GND


You would need to configure the pin as a digital input and provide a pull-up resistor to Vdd.


  Accept a input switched to 30VDC


You would need to configure the pin as a digital input and use two resistors to form a voltage divider.


  Accept a 0-15vdc analog input


You would need to configure the pin as a analog input and use two resistors to form a voltage divider.


  Provide a Analog output 0-15vdc


This is the one configuration that is probably not possible on any arbitrary pin, as the DAC outputs can only appear on ports PA4 and PA5.


  Provide a Digital out of either 5v or 12v selectable through software.


You would need to configure the pin as a digital output and use external transistors (or an analog switch) to switch between the two voltages.


  Provide a Ground for external sensors.


You could alternately configure the pin as an input (tristate) or digital output 0 (ground).

You could provide all of these options at the same time, and select which one to use via a Berg connector (jumper).  The analog functionality is limited to the 16 pins that can be remapped to the 16 channels of the two ADCs.