Did you get the email from Qantas that said:
"Dear XXXXXX,
For the first-time, you can transfer your American Express® Membership Rewards points into Qantas Points.
And for a limited time,
earn 20% more Qantas Points when you transfer your American Express Membership Rewards points to Qantas Points*. Offer ends 30 June 2019.
Now your American Express® card can take you that extra mile."
Or maybe you didn't even need to get the email!
FrequentMiler reported on the stacking possibility, and one comment verified that it stacked for them. That's a really nice haul!