"I simply maintain that companies should retain the capability to provide the government unencrypted copies of communications and data stored on devices, when a court orders them to do so."
So what does this really mean?
For the moment, let's ignore companies and individuals storing their own information on their own equipment and focus on what these proposals are focussed on: online 'cloud' providers and mobile device/software vendors which store and transmit data on behalf of end users.
The upshot is that Rosenstein's proposal would prevent such companies from offering real 'zero knowledge' encryption either in transit or at rest.
Rosenstein (and the rest of the mob around the world) know full well that asking companies to store the plaintext copies is unacceptable and I am sure they know why that is the case. This is not a serious proposal: it is simply a doubling-down on their stance: they demand access to plaintext so if the providers won't agree to facilitate decryption, they must store data in such a way that it doesn't require decryption.
It is not a clueless attempt at a compromise: it is an ultimatum.