This is pure hypothetical, but I've wondered what would happen if apple were to lose in court, then make this custom iOS signed to work only on the specific phone in question, and provide the installer to the FBI with a bill for $5 million in development time. Then destroy all source on this special version, stating that they don't feel comfortable having that in their source tree since a rogue employee might leak it. Then the next time there is a phone to crack, they build the custom version again, an provide it to the FBI with another $5 million bill for services rendered since all development would have to be done from scratch. That would at least provide a bar that law enforcement would have to pay, rather than simply thinking once the cost is born once, future versions are cheap like $10k.