Q: It seems that the new part 147 is a done deal, but the publication says the comment period is open until 9/21/22. Should we comment?

A: The short answer is YES, we expect and encourage the community to comment on the interim final rule.

Long answer: Since Congress mandated that the FAA publish this very specific language, the agency has very little leeway to change the text. That said, Congress also directed the agency to issue the language as an "interim final rule," not a "final rule," meaning Congress also intended the agency to take public comment once the "final" rule was published. So, comments are encouraged and could potentially direct changes to the text if there was a very compelling reason. If additional rulemaking is deemed necessary given public comment, more likely the FAA would initiate a new rulemaking.

The FAA addresses this question and more in its FAQ document.

Q: Would you please clarify the effective dates for the PTS and the ACS? Both FAA-S-8081-26B (PTS) and FAA-S-ACS-1 (ACS) state on the cover page the same effectivity date and enforceable statement. Which of the two will be used to comply with the new part 147?  

A: The “new” FAA-S-8081-26B (PTS) was created to combine the current PTS into one document and will still be the testing standard through next summer. Upon the new part 147 effective date (Sept. 21, 2022), the school will be required to align its curriculum with the ACS (i.e., the ACS will be the curriculum standard).
 
So, to answer your question, both standards will be effective for different purposes (PTS for testing, ACS for curriculum) for the next year. The FAA will officially adopt the ACS as both the testing and the curriculum standard on July 31, 2023, at which time the PTS will phase out.
 
You’ll find the rationale for this “transition plan” on page 35 and 36 of the interim final rule, along with this statement: “…the FAA will use the Mechanic PTS as the testing standard until July 31, 2023. After July 31, 2023, the FAA will use the Mechanic ACS to conduct mechanic tests.”