What I am about to write here is similar to third hand information.
  I do not have first hand experience.

  I looked into putting an audio loop into a venue.  I asked an audiologist
  about the prevalence of T-coil equipped hearing aids.  She told me most
  users prefer small and rechargeable.  There is not much space in the unit
  and rechargeable would likely be selected.  So, the T-coil does not get
  included.  She thought T-coil units were common in Europe.

  There are special amplifiers to drive the audio loop.  The makers don't
  tell us much about them.  I think we would call those transconductance
  amplifiers.  Reading the subject article is encouraging.  Perhaps we
  will just try this after the virus is not such a threat.