I asked the same question one of the very reputable lawyers. I am posting my question and his answer which makes it look like filing a lawsuit against FBI is a reality.
"I am waiting for adjudication of my employment-based Adjustment of status (I485) application for over 2.5 years. I am in EB1 - Outstanding Researcher category which is still current in terms of visa availability. My application is past the current processing times published for I485 at Vermont Service Center for over a year-and-a- half. I did several inquiries with USCIS and got a reply of pending security checks. I would guess that would be FBI Name Check. It looks like the Records division of FBI is severely backlogged with security checks with some portion of them taking over three years to complete. Is there a way to force these two government organizations involved to do their job and to finish these tasks which are taking them way beyond reasonable expectations? Looking at initiating some legal complaint I read about filing a writ of mandamus lawsuit in court against USCIS. I wonder if pending security checks issue will cause this lawsuit to be dismissed and if so are there any legal ways to pursue against the FBI Records division?"
Here is his answer:
"I'm about to file a case against the FBI and USCIS on a case just like this. I think that's the only thing that will shake it loose."