According to reporting, they have actually done this before.
Most of the discussion I’ve read about this is along the lines of: clone the drive on the phone and then brute force the clones (circumventing the lockout issue: if you get locked out just keep trying on a new clone).
In a relatively famous case, the FBI cracked the password on the San Bernardino shooter’s phone, but did not explain how they did it: https://www.vox.com/2016/3/29/11325134/apple-iphone-fbi-san-bernardino-case-ends
Here is a company selling a brute force module for iPhones, although they don’t explain how they get around the lockout issue: https://belkasoft.com/unlocking-ios-devices-with-brute-force
Here is another article about a company that claims to be able to brute force iPhone passcodes: https://www.vice.com/en/article/how-to-brute-force-iphones-graykey/
There are at least 37 of us. Unless a bot posted this…