Is it possible to develop and debug software for a microchip ARM controller in MPLABX?
Here the answer from microchip:
MPLAB X IDE v5.05 has beta support for 16 SAM devices. These are the devices that are currently beta supported under MPLAB X IDE v5.05:
ATSAMV71Q21 ATSAMS70Q21B ATSAMS70Q20B ATSAMS70N21B ATSAMS70N20B ATSAMS70J21B ATSAMS70J20B ATSAME70Q21B ATSAME70Q20B ATSAME70N21B ATSAME70N20B ATSAME70J21B ATSAME70J20B ATSAMD21J18A ATSAMD20J18 ATSAMC21N18A
Please continue using Atmel Studio for SAM Devices, till MPLAB X doesn't fully support the ARM devices. More details about the Atmel Studio ecosystem cab be found here: http://www.microchip.com/mplab/avr-support