So IF you registered your weapon with a pistol brace the ATF is not:

1. Issuing a stamp. It is just based on the engraved serial #s.
2. Not requiring you to engrave the receiver.

Sooooooo my question is:

IF they are not doing all that, then is there a possibility that they will simply revoke the stamp at some point? Really curious about how this is going to play out.

From what I have read.  You actually receive a copy of an approved form one, but no stamp due to the tax not being paid. And no engraving required, I believe it was referred to as title 1 markings, would be used.

I don't think there is any language in the rule which specifically says that they will never come after anybody after they register the SBR. Even if there WAS such language, I trust the AFT as far as I could throw your average hippopotamus.

I mean, you ARE admitting to a felony, which is why you need "amnesty". Normally the process is submit Form 1 or 4, wait (a long time), get approved, THEN build or take possession of SBR. With this thing, you're admitting to having an unregistered SBR BEFORE registration.

For this, and several other reasons, biting the cheese on these "free tax stamp" SBR's is a terrible idea IMO. YMMV.