State income tax

I thought that it was the case, and a quick check seems to confirm, that while the federal government has first bite of the cherry the states could still levy income tax, though it might be impractical to do so, and that the federal government could in turn deny them grants.

This doesn't make it impossible though for the states to levy income tax and would address the narrow tax base with which the states currently operate. And apparently the states collecting an income tax surcharge via the ATO is being considered by the Henry Tax Review.

Aside from addressing the narrow tax base this is a good idea because it would mean the states would not be as reliant on indirect taxes which are inherently regressive. Though what is meant by a surcharge would have to be developed.

However the suggestion to remove stamp duty seems to be an effort to move more of the costs of speculation on to those who don't speculate, generally those who can't afford to do so. It would facilitate idle speculation at the expense of those who are productive.