Aussie. No. It was mandatory. I removed the mandatory reqirement when I became chairman in 1991.
It was mandatory full position reporting above 5000' because IFR and VFR flew at the same levels.
So it wasn't mandatory! Except if you went over 5000'. So what I did all those years ago, heading out without a lodged flight plan was actually legal. I thought so at the time anyway.
BTW, I agree with your post. I still remember the ninnies at the (CAsA) meetings stating how the countryside would be littered with missing aviators because we were moving away from full reporting. Wonder where they are now?