I doubt that Glock and Sig will buy in, they are simply too big and have too many lucrative contracts. There are levers to move the other two. Smith & Wesson was basically destroyed when private sales collapsed after their cloak-and-dagger deal with the Clinton JD, so they may still be sensitive of private sales and receptive to pressure. Ruger has Bill Ruger’s selfish collusion with Clinton in the matter of the AWB-which, IMHO was never paid for-to live down.
Fom what I've seen, for the vast majority of these companies, the civilian market completely dwarfs their government contracts. They'd do better to look at what happened with S&W a few years ago.
Bill Ruger is (fortunately) dead and the current management of the company has zero interest in following in his footsteps in that regard. I wouldn’t take a free Ruger product from the old Ruger, but the new management has managed to sell me an SR556.