I am not sure if it is true - but I was told/read somewhere that if all income in Aus was taxed at a flat rate of 10% with NO DEDUCTIONS allowed then it would be more money than the total tax haul. I would be happy with that setup. And so simple too - but I don't think accountants would be too pleased. Not sure if anyone knows how to do the sums on that to check.
I was also told/read that if the 10 wealthiest Australians payed 45% of their earingings in tax that it would roughly equal the entire current tax haul. Again no idea if the figures are true though.