It looks like the ATF is just begging for another Waco, TX type of incident.
https://www.firearmspolicy.org/atf-to-issue-guidance-stabilizing-braces
https://www.firearmspolicy.org/atf-to-issue-guidance-stabilizing-braces
Firearms Policy Coalition
BREAKING: ATF to Issue Guidance on “Stabilizing Braces”
FPC believes that the NFA is an unconstitutional infringement of the People’s rights, that the ATF should be abolished, and that any policy or practice enforcing the Act is unconstitutional and immoral.