The cat's out of the bag. All this would lead to is law-abiding citizens having their information at risk while criminals continue to use crypto without backdoors.
It would be trivial to have terror cells be distributed a USB with several GB of a OTP, and that would be unbreakable even into the age of quantum computing if used properly.
Thus isn't at all about terrorism or the "really bad guys." It's 100% about accessing the average Joe Blow's communications.
If the government can’t crack strong encryption as-is, the problem is that strong encryption is deployed at scale.
Removing strong encryption at scale would have far more effect than what you’ve described.