I signed up with the ATF for emails from them, and I got this.

The Bureau of Alcohol, Tobacco, Firearms and Explosives
Objective Factors for Classifying Weapons with “Stabilizing Braces”




GENERAL NOTICE
Objective Factors for Classifying Weapons with “Stabilizing Braces”

US Bureau of Alcohol, Tobacco, Firearms and Explosives
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ATF is publishing the objective factors it considers when evaluating firearms with an attached stabilizing brace to determine whether they are considered firearms under the National Firearms Act (NFA) and/or the Gun Control Act.

ATF publishes this notice to inform and invite comment from the industry and public on the proposed guidance prior to issuing a final document.  Upon issuance of final guidance, ATF will provide additional information to aid persons and companies in complying with federal laws and regulations.

This notice also outlines ATF’s enforcement priorities regarding persons who, prior to publication of this notice, made or acquired, in good faith, firearms equipped with a stabilized brace.

Finally, this notice previews ATF’s and the Department of Justice’s plan to subsequently implement a separate process for current possessors of stabilizer-equipped firearms to choose to register such firearms in compliance with the NFA, including an expedited application process and the retroactive exemption of such firearms from the collection of NFA taxes.
Read the general notice
Submit a Comment by January 4

You may submit comments, identified by docket number ATF 2020R-10, by any of the following methods:

   Federal eRulemaking Portal: www.regulations.gov. Follow the instructions for submitting comments.
   Mail: Office of Regulatory Affairs, Enforcement Programs and Services, Bureau of Alcohol, Tobacco, Firearms, and Explosives, 99 New York Ave. NE, Mail Stop 6N-518, Washington, DC 20226; ATTN: ATF 2020R-10
   Fax: (202) 648-9741

All comments must reference this document's docket number (ATF 2020R-10), be legible, and include the commenter's complete first and last name and full mailing address. ATF will not consider, or respond to, comments that do not meet these requirements or comments containing excessive profanity.

Written comments must be postmarked and electronic comments must be submitted on or before January 4, 2021. All properly completed comments received will be posted without change to the Federal eRulemaking portal, www.regulations.gov, including any personal information provided.
Submit a formal comment

https://www.federalregister.gov/documents/2020/12/18/2020-27857/objective-factors-for-classifying-weapons-with-stabilizing-braces

It doesn’t look like they submitted any “rules” to comment on.

They just say they’ll decide what’s legal on a case by case basis.

Guess they dont want comments now

https://www.atf.gov/firearms/docs/general-notice/sb-criteria-withdrawal-notice-12-23-20pdf