UPDATE
The answer is so small a probability as to be unmeasureable in statistical form and the claimed enhanced safety does not justify the expense.
The only mob who can gain measureable benefits are Airservices.
Occurrence Number: 200800771
On 13 February 2008, a Piper Aircraft Corporation Super Cub aeroplane and a Robinson Helicopter Company R44 Raven helicopter collided in midair during feral goat culling operations. The aeroplane impacted the ground at a steep angle, fatally injuring the two occupants. The helicopter, though damaged, was safely landed.
The investigation is continuing.
ADS-B IN aural would not have helped?
Lucky we know
Statistically there is no measurable risk of mid air collision in class G airspace.