Thanks for bringing this to our attention! This development is worth watching. According to Cointelegraph, it isn't a law just yet. The bill has been sent to Arizona’s House of Representatives for a vote. If it passes the House, it will become a law.
"If the bill is adopted, Arizona would become the first state in the U.S. to accept cryptocurrency tax payments by the year of 2020, as stated on the public record. The bill would allow taxpayers of the state to use “a payment gateway, such as Bitcoin, Litecoin or any other cryptocurrency recognized by the department, using electronic peer-to-peer systems.”
https://cointelegraph.com/news/us-arizona-senate-passes-bill-to-allow-tax-payments-in-bitcoin
So while it isn't set in stone yet, it looks promising. Thanks for the heads up!