Sunday and public holiday penalty rates will be reduced, page-13

As a past employer I'm not sure it will make a lot of difference.
What is the difference in dollar terms for a Sunday?
About $5 an hour plus other outgoings isn't it?
So for a 6 hour shift a saving of $30 per employee.

They say it will encourage some businesses which choose to remain closed on Sundays to now open.

Well first you need customers to service - some places don't open because their customers aren't in the area on weekends.

Others businesses in areas where there are customers don't open because it's not profitable enough to do so.
If they start opening that may lead to more businesses competing for the same customers, spreading the income.

On the other hand there are businesses that are crowded on Sundays, employing lots of staff.
They might put on an extra person or pocket extra profit.