An interesting topic, this one, especially as I own an English
(I assume) Aeolian half-Duo-Art upright which has keys that _do_
move, presumably modified at some point in its life.

There could be something in this 'lack of fast repetition' which it is
alleged 'moving pianos' suffer from; mine certainly isn't up to playing
parts of some of the QRS rolls (on the brown paper with small holes) at
the suggested speed, and it consistently struggles on many rolls with
what I believe is described as the 'mandolin' effect, unless pedalled
at full tilt.

However, as a counter-viewpoint to those who claim it only amuses kids,
I spent a while yesterday studying the effect of a demonstration model
modern Yamaha midi disc-operated piano with moving keys at my local
Dixons store in Birmingham, and also another one at Beatties in
Wolverhampton.  It was very interesting to note the many adults who did
a double-take at the piano 'playing itself'-- and stood to watch and
listen for a while, where they had been ready to walk past -- the thing
that always caught their attention was not the music (good though it
was) but the moving keys!  Even in this age of virtual everything it
was still something which many passers-by found fascinating.

I do sometimes wonder whether it is possible to build some kind of
locking device which can be enabled or disabled at will without having
to alter the piano greatly.  I am loathe to pull keys off and start
fiddling around with weights.  But it would be nice to occasionally
play a fast roll and hear all the notes!

Cheers,
Nicholas Newble