They are suing under statutes that normal citizens and second amendment foundations cannot. They are suing states under deprivation of constitutional rights and the deprivation of rights by law-enforcement. Those specific statutes or lawsuits have not been tried yet.
That's an argument, but a really bad one. Sure, they're suing under 34USC12601. That is indeed not available to individuals or associations. Those have to use 26USC1393 and friends, which I'm very familiar with (having been a party). But that argument is one about the color of the lipstick on this particular pig. Underneath both 12601 and 1393 lies the same fact pattern: plaintiff has to demonstrate "that deprives persons of rights, privileges, or immunities secured or protected by the Constitution or laws of the United States" (quote from 12601, 1393 has substantially the same requirement). And the cases under 1393 were not won, because plaintiffs were unable to demonstrate that there is a right to keep or bear a Glock, or an off-roster pistol. The US DoJ is facing exactly the same question, and logically the answer will have to be the same. This is
res judicata.
Now your point that
Hemani might have changed things since
Boland was first put on hold. That's absolutely true. And the sensible vehicle for taking advantage of that would be
Boland, since it is already teed up, waiting for the Supreme Court to cross the i and dot the t (or something like that). At the underlying level, this new lawsuit doesn't add anything that isn't already in
Boland, which is several years ahead in its progress. The best case is that this new case goes up to the 9th circuit, where it will be merged with
Boland ... and we're back where we are right now, having wasted some judge's time and resources.
(Side remark: Autocorrect likes to mess with Hemani.)