Conventional jet engines run at RPMs in excess of 20000rpm. To get this same speeds for the same mass flown rates of say a J79 (F4-Phantom) you'd be looking at

Conventional jet engines run at RPMs in excess of 20000rpm. To get this same speeds for the same mass flown rates of say a J79 (F4-Phantom) you'd be looking at some massive electric motors. Conventional jet engines would be using electric motors if they were light enough already. There is a reason Rolls-Royce UltraFan uses a speed reducing gearbox for it's fan blades and not an electric motor. More to the point above, at hypersonic speeds, using a conventional compressor is sort or useless unless you can keep your air cool.