Still in play IIRC. They’re being sold, so that apparently is legal for now, but the game ain’t quite over yet. If the final SCOTUS ruling makes them illegal, simply toss the brace and you have an AR pistol with the buffer tube sticking out the back. An alternative is a PCC with a folding stock and a 16” barrel or one with a pinned and welded muzzle device that makes the barrel 16” long.
I gave a sort of short answer but it’s really the truth. Lots of variables. As pappy says it ain’t fully decided. But something you might consider is buying a “pistol” intended receiver and wait for something definite to shake out. It can be used for either pistol or rifle builds. And again as pappy says you can always do a pistol with an exposed buffer tube. My intended use for an AR pistol would be for a concealed carry legal 30 round pistol to keep in a vehicle. For that use the exposed tube wouldn’t be a deal killer though a brace would be nice.