We do have several local taxes as well (in France). They are all handled by your equivalent of the IRS, everything is on the same web site (I do not even know what I pay in local taxes, I get an email telling me that it i due, and it is then direct debited from by bank account).
Yes, but you have a unitary government. In the US, states have a constitutional authority to independently administer taxes inside of their borders, and there is no way in hell that they are going volunteer that power away. Also, states have the power to tax income that is generated outside of their borders where have no power to require reporting. So they couldn't legally automate those tax filings even if they wanted to.
The US government has zero power to change any of this.
