I've heard that one too.Sounds very similar to the old Super...

I've heard that one too.
Sounds very similar to the old Super Surcharge days, which were a nightmare to administer and a strong disincentive to contribute. There would be admin issues with rate of deduction for the payer / employer.
Increasing the tax rate above 15% potentially means that $100 going in would reduce to $68.50. Then if paid out < age 55 or to an adult child, taxed again at 16.5% = $57.20 in hand.
As previously mentioned, most of the deduction limit for this person would be used up by SGC payments so they wouldn't have any choice on the matter.

My view is to keep things as simple and unchanged as possible and hope the govt gives super a rest from their communist ideology and vote-buying.