This "going dark" scenario would require new legislation. With secure enclaves, modern smartphones can't be cracked open in the manner that the FBI wanted in the 2016 case. So there's no such thing as "court order tech company to crack phone" anymore. It would have to be "outlaw tech companies from producing phones that they can't crack open", which is very different and does not fall under any existing US statute.

Congress would pass that law in a heartbeat.