I just saw an interview with more detail and it sounded to me like they were going to have the turbine drive a generator powering an electric motor to drive the fan. Like a diesel electric locomotive. And this is supposed to allow it to transition from turbofan to turbojet to reach mach 2.7 to allow starting up a ramjet which launches the second stage to mach 5 before lighting its rocket engine. Not sure why none of that detail was mentioned here.
The ramjet is on the second stage, separate from the turbofan/jet on the first stage.
The loss in the electrical system should be pretty small, and they claim that they gain a lot of efficiency from being able to optimize the engine over the whole range from 0 to mach 2.7.
Yes and no. An electric compressor doesn't mean the turbine doesn't drive the fan. (It might make pre-cooling easier.)