From the horse's mouth, the ATF's page on it:
https://www.atf.gov/rules-and-regulations/factoring-criteria-firearms-attached-stabilizing-bracesimo this is both better and worse than the memo they published last year, just goes to show they've been working on this for a while. Better from a technical standpoint because it actually enumerates some measurements, worse because the way it lays out criteria practically every braced AR pistol becomes an SBR.
On the plus side if they actually did this it's practically guaranteed to get SBRs off the NFA thanks to Heller. They say there are at least 3 million in circulation, just based on sales they know of in that configuration.
