Hope this thread's not too old to add my bit, perhaps looking from another
viewpoint:

The earliest players were all mechanical - vibrating hammer barrel pianos,
kicking-shoe mechanisms, etc. All of these could be electrically-powered
simply by addition of a motor and a drive belt. Some later kicking-shoe
mechanisms such as the Electrelle were completely electrical, with a
motor-driven rotating shaft and a tiny solenoid operated by direct
electrical reading of an ordinary 65-note roll, dropping the shoe onto the
roller to play the note (exactly the same powering mechanism as an
electric typewriter).

The new 'Rye Treasury' Museum here in the UK has a specimen (probably not
an Electrelle but a clone) of perhaps 1908 vintage, a retro-fit into an
ordinary piano - the mechanism is very compact. Given the typewriter
analogy, it is interesting that this specimen uses uninked typewriter
ribbon to connect the kicking shoes, mounted  at the top of the case, to
the ordinary piano action! Red ribbon in the treble, black in the bass.
Three hand levers are connected to rods which stretch these ribbons so
pulling the hammers forward, to give some dynamic control.

So, pneumatic systems weren't kept by default, they were specifically
developed for player piano use. I am sure the reason for this was to let
you _play_ the instrument, not just listen to it play itself. The player
piano was developed as an artistic musical instrument, not a mechanical
one, and the pneumatic player is an exceedingly good design for user
control. To this day nothing has been developed that's better for the job
of letting a non-pianist play a piano (of course, this capability is
irrelevant for owners who don't want to make music for themselves).

In essence, reproducing players simply automated what a pianolist did -
varying stack suction to control dynamics. Again, the controllability of
the pneumatic player made it the right solution for the technology of the
time.

Only with the control capabilities of electronic (as opposed to electro-
mechanical) systems has electricity supplanted air as the best activation
system. I understand that the Pianocorder was consciously an electronic
copy of the Duo-Art, with a theme-accompaniment system and a split stack.
Only with 80s technology did we get direct control of each note's dynamics
- even then, upright Disklaviers had only about half the dynamic range of
a good player (have the later ones been beefed up?). The Bosendorfer SE
was the real bees knees - what a pity it's not made any more. Anyone got a
spare going (very) cheap?

I'm not aware of any commercial MIDI products that allow interactive
control of dynamics, tempo, rhythm, pedalling, etc. I guess there's no
demand. Rex Lawson's roll editor computer has an attachment with all the
usual pianola controls, but that's for playing non-MIDI masters with no
dynamic data into a piano module. Perhaps it's something that could be
adopted for a MIDI pianola?

[BTW Although mentioning gas and hampster power, Jeffrey Borinsky (MMD 7
July) forget to mention the early experiments with inflatable players,
such as the Airiola. These were thought valuable for the average tiny
English house as they could be let down and stored in a cupboard when not
in use. Sadly both snakebites and the pin-end rolls then in use tended to
puncture them and they went flat. They must be rare today, and I would be
surprised to find one in any MMDer's collection. <G>]

Julian Dyer