Android, at least the parts that would be required to be modified to implement this misfeature, is already open source. That won't help. The DoJ isn't asking for proprietary code secrecy, fundamentally they're asking for key escrow. Storing data in different places isn't something source visibility can address.
Which they will. All they are asking for is some form of key escrow; which can (and has) been given a reasonable security definition.
The problem is that secure implementations of key escrow are much harder; and (given the amount of use the escrowed key will get), certainly going to be broken in practice.