The way I read it (from various Qantas emails and notifications, along with anecdotal evidence):
For paid Qantas, Qantas Group and Qantas Partner tickets booked via Qantas prior to March 10, 2020:
Bookings cancelled "up to" March 31 2020 (I'm assuming it means March 31 2020 23:59:59) for existing travel bookings up to May 31, 2020 (which may be confusing if your actual fight departure time is June 1 2020 1:00 am for example):
Option 1: Cancel and request equivalent value credit voucher. Voucher valid for use 12 months from date of original ticket*. When voucher is used, change fees are waived. (i.e "Free Change")
"For use" is ambiguous but my understanding is in this case it means booked and travel commenced.
There's a lot of people confused with this particular "clause", as the Qantas help desk and call center have been giving differing advice. Some pax have been told 12 months to re-book, others are told travel must commence with 12 months from the original ticket date.
Option 2: Cancel and request refund. Refund is minus any applicable charges as per fare conditions of original ticket. (Not a "Free Cancellation" unless your original fare allows)
Bookings cancelled after March 31, 2020
Option 1: Cancel and request equivalent value credit voucher. Voucher valid for 12 months from date of original ticket*. When voucher is used, change fees are applied. (Not a "Free Cancellation")
Option 2: Cancel and request refund. Refund is minus any applicable charges as per fare conditions of original ticket.(Not a "Free Cancellation" unless your original fare allows)
For points tickets:
Bookings cancelled up to March 31 2020 for existing travel up to May 31, 2020.
Option 1: Cancel and pay the points cancellation fee. Taxes, charges etc are refunded. (Not a "Free Cancellation")
Option 2: Change the date of travel and the change fees are waived. (i.e "Free Change")
Bookings cancelled after March 31, 2020
Option 1: Cancel and pay the points cancellation fee. Taxes, charges etc are refunded. (Not a "Free Cancellation")
Option 2: Change the date of travel and pay the change fee. (Not a "Free Change")
*Vouchers from cancelled Jetstar flights must instead be spent within six months of the cancellation being actioned – not six months from the date of original purchase – and can be used for travel within 12 months of the new booking date
Now, I have also read that if you make a booking after March 10 and before March 31 for travel up to May 31, 2020 on Qantas or Jetstar, all cancellation fees are waived for bookings cancelled up to May 31, 2020 and your voucher has the same restrictions as above. ("Free Change")
So, in summary:
If you booked before March 10 for travel up to May 31, you have until March 31 to action the "free change" and
If you booked after March 10 for travel up to May 31, you have until the date of travel to action the "free change".
In reality, there is no free cancellation (unless your original fare conditions allow this), there is only a "free change" under certain conditions.