In order for it to be practical the frequency of current must yield an inductive impedance about 10x to 100x the DCR of the wire. Otherwise it will not work. even at 50MHz it won't work unless highly tuned with heavy copper thin hollow core conduit. Then skin effects and RPM , inertial mass, imbalance etc make it impossible.
Thus the core in a generator must have a magnetization flux to couple the magnetic field thru the commutation DCR to gérante any appreciable power, otherwise the inductive impedance will just shunt or short out the magnetic field and generate very little voltage or current. This can be done with permanent magnets, laminated iron core with an excitation field current to increase voltage etc.