What is the FAA's official outlet for informing the public of permanent, systemic changes?
The FAA has multiple email groups you can subscribe to.

https://public.govdelivery.com/accounts/USAFAA/subscriber/new?topic_id=USAFAA

Click the link and you will be brought to a page where you can provide your email address.





You will then be brought to a page where you can select the email groups you want to subscribe to.