Which is, of course, the case in everything because of finite resources and other, less economic, reasons. I don't think there is a question that they will have to make choices that they didn't have to make before. What these choices are, I certainly do not know, but given the level of active enforcement of things like magazine bans and AR feature bans, even at levels where it is much easier to do it, I don't really see the ATF bothering to send manpower in to Buttfuck, ID to search for pistol brace offenders.
I don't see any other way to analyze what will happen other than based on what the same group has done in very similar situations.