Actually the FBI's current argument is very close to saying that the All Writs Act has no limits, and can compel literally anything the FBI thinks would "help" them with investigations.
The FBI's argument doesn't come anywhere close to saying that. What the FBI's motion actually says[1] is:
Pursuant to the All Writs Act, the Court has the power, "in aid of a valid warrant, to order a third party to provide nonburdensome technical assistance to law enforcement officers."
The most important limitation here is that nobody, including the FBI, is claiming the All Writs Act grants the court any power at all in the absence of a search warrant. Nobody really disputes the statement above, or the validity of the warrant in question.
Again: if the FBI wants Apple to preemptively insert a generalized backdoor into their products they'll need to lobby to have new legislation passed. They've tried that and it hasn't gone much of anywhere. In my opinion lets try and keep it that way.
I'm not a lawyer so obviously I'm not exhaustively well read on the law but in the case that All Writs did allow any action to be demanded to help with an investigation it would still require there to be an investigation in the first place.
To preemptively demand a back door is almost akin to guilty until proven innocent, youre assuming that there will be an investigation in the future where a governments ability to hack a device is required.
