Restricting fabrication files would be a lot harder, technically, than most people think. The fundamental construction of a firearm receiver isn’t that complex to build from paper records in Solidworks or Inventor, and there’s a ludicrous amount of those out there. To block people from designing from first principles, you’d have. Yes, the .gov tries to limit access to copyrighted files or sex trafficking, but it’s not actually that effective at them, and much of the extent it can successful go after online drug sales is because of the money aspect.
The fabrication equipment might be easier to restrict, at least partially. In addition to involving the transfer of funds, even small 3D printers necessarily still aren’t exactly the sort of thing you can hide in a book cover. But I can’t see the political willpower to do that on a significant scale, not after ten years of actively promoting them as the Next Big Thing. Maybe that’ll change as metalworking skills continue to fall out of common knowledge, though.
Smokeless powder (and even more so, primers!) are going to be a lot longer term a thing, if ever. Even the existing giant bulk production facilities with highly specialized equipment have a rough time of things, and there’s been a decades-long effort to neuter home chemistry from the grade school up. That said, there might be progress with dual-use alternative tools, or even inefficient but high-profile electric-powered ‘firearms’, though, which would resist regulation pretty readily.
The defense/offense recalculation will be tough. Type 3 and 4 plates can already stop almost all sidearms, and the extent that they haven’t already forced a change in tactics is simply that they’re woefully impractical to wear anywhere and can’t usefully protect the face. If assist motors change that, it’ll be a big deal. On the other hand, recoil considerations have already begun pushing people away from big handgun rounds, even if not to the extent of rolling back to .38 SPL –unless you’re in Hollywood on the wrong day, you’re just not that likely to run into that sort of threat.
I think one of the big areas of interest will be less-lethal weapons. There’s been some development in the mil sector, but the commercial and civilian field is strangely moribund. The basic operation of Tasers goes back forty years, and pepper sprays even older than that, and it shows. Worse, most of the attempts to evolve these tools have focused on political compliance (such as the taser “confetti”) rather than improving effectiveness, at the same time that more and more concerns have popped up about unwanted secondary effects. The less said about conventional flashbangs the better. So there’s a lot of low-hanging fruit.
Remote-operated weapons have been of concern for a while, highlighted by the Dallas use of a bomb squad robot. There are some technical reasons that I’d expect (and hope!) truly autonomous armed robots don’t enter the civilian sphere any time soon, but combined with less-lethal weapon development and I’d expect to see some interesting stuff pop up, for good and for ill.