I heard an interview around New Years that said the new rule had not been signed by the acting Attorney General and the Govt Shutdown meant that it would not be entered into the federal register. Apparently, the clock starts ticking (90 days?) when it is written into the federal register. Also, the fact that an acting Attorney General who had not been approved by the Senate would sign it was one of the things they would sue about. If the order has not yet been signed, that might be the reason. Waiting on the Senate to confirm the new AG.
That was a month ago. With everyone focused on Shot Show, I haven't heard anyone mention this except in general terms.
The lawyer from that interview suggested everyone hold on to their bump stocks. He said there were several different reasons a judge should stop or reject this rule change. One was they didn't properly follow set procedures on implementing new rules. Apparently, that has been used to throw out regulations in the past.