From Supercoach site tonight:
Will there be any changes to help us navigate the extra byes?
With each of the eight Opening Round teams having an early bye in rounds 2, 3, 5 and 6 (two teams per respective round), Best 18 scoring will apply for these rounds. To assist with the new challenge of managing these early bye rounds, an additional 4 trades will be added, for a total of 40 trades available for the season. Note that the usual maximum of 2 trades per round will continue to apply in these early bye rounds. Up to 5 Trade Boosts will also be available once again.
They then mention 3 trades per round for mid-season byes.