It looks like revenue ruling 2019-24 was released on Wednesday 09 October 2019.
It explains that when a cryptocurrency forks if you receive any new cryptocurrency that can be traded for dollars you have a basis in the new crypto that is the fair market value at the time of receipt. You also have taxable income equal to the fair market value of the new crypto received.
What should be done about airdrops from tax years prior to 2019 if you didn't calculate basis and income this way?
Resource:
Airdrop IR-2019-167 RR 2019-24
https://www.irs.gov/newsroom/virtual-currency-irs-issues-additional-guidance-on-tax-treatment-and-re...
Related question:
Should I report bitcoin cash?
https://ttlc.intuit.com/community/taxes/discussion/should-i-report-bitcoin-cash-received-in-the-bitc...
