Not sure exactly when they changed but I noticed new plastic trolleys in Dickson today. I have my doubts that entirely replacing a fleet of salvageable metal trolleys with plastic ones (even if recycled plastics) is actually "pushing for a greener future".
I remember Target went plastic trolleys for a stint. They didn't really go the distance.
If I recall correctly Woolworths had also tried this with Big W trolleys though all evidence of this appears to be scrubbed from the internet.