Seems like you could get many of the benefits of a ribbon by using a laser to measure the vibration of the ribbon vs measuring the voltage. Of course the ribbon won't vibrate the same without a magnetic field applied so you could still supply that. You'll also just be picking up the vibrations at one point of the ribbon instead of the summation(?) of it's movement. But you won't have to worry so much about noise and shielding, while still retaining a low resonant frequency.
You might be able to use a laser, with a video camera as the sensor. Even though the frame rate of the camera is much less than the sampling rate required for audio, it potentially has a high enough spatial resolution that there are multiple pixels per audio wavelength, giving enough bits of information per unit time. Some smart maths, effectively modelling the ribbon and matching its response to the observation, would be required. In this way, the vibration of the whole ribbon might be measured.
