The application of automatic playing is much simpler using MIDI than
any other method.  Since electricity is mandated, the use of solenoid
actuators would be fairly simple.  Several builders of pipe organ
controls offer solid-state MIDI switching units in 12-note increments.

If you're interested in electrifying a player instrument, then it
becomes even easier.  A pressure instrument like an Aeolian Orchestrelle
can be 'MIDIfied' by simply adding Wicks Direct Electric valves or
similar to the key channels.  Some links:

  http://www.tiac.net/users/ztronics/
  http://www.artisan-instruments.com/
  http://www.emutek.com/organ/organ.htm
  http://www.petersonemp.com/
  http://www.westacott.com/
  http://www.borg.com/~jglatt/tech/pc_intfc.htm
  http://www.midiator.com/
  http://machines.hyperreal.org/categories/DIY/schematics/

Have fun!

Regards,
Bob Loesch - in beautiful Lake County, California, USA
http://www.jps.net/rrloesch