I find the discussion posed as MIDI files vs. music rolls meaningless.
More appropriate would be MIDI files as an adjunct to music rolls.

They are not mutually exclusive in any way.  Depending on the
application, there may be any percentage of overlap.  Both data systems
have their advantages in specific applications.  Rather than an "all
one or the other" choice, it's more about two systems that can
complement each another, and data may flow in either direction.

I use MIDI files of roll scans to drive my Pianocorder.  While this has
many advantages like continuous music, being able to edit files for
best playback (*), no rolls to rewind, removing from service old rolls
that are no longer safe to play, etc., it's still fun to actually
physically play a roll on the pneumatic player and be able to vary the
speed and expression and still be amazed and delighted at the sheer
brilliance of the engineering and mechanics of the system.

I think I got the most enjoyment out of my roll player when I was
rebuilding it.  It was exciting to look forward to playing a roll each
day after the latest batch of rebuilt pneumatics  had been installed
the night before.  To see the system come alive and actually work was
just amazing.

Likewise when I made up my Pianocorder Obensetzer, a lot of the fun
and excitement was transferring the piano rolls into MIDI format and
manipulating them for the Pianocorder, and then playing the results.

(*) "Garbage in, Garbage out".  I have come to the conclusion that
much of the Pianocorder library that does not play well on the
Pianocorder is the fault with the data on the tapes.  A well adjusted,
good arrangement, while not able to realize the range of expression as
on a reproducing piano, can still produce excellent music.

It's all about the data the Pianocorder has to work from.  I have found
the Pianocorder system has two weaknesses compared to a reproducing
piano.  Range of expression is somewhat limited, and the Pianocorder
cannot duplicate the faster repetition of a pneumatic player.  Taking
these two limitations in mind, with proper adjustment and a good
arrangement to start with, the system can still make some mighty fine
music.

Tom Lear
San Francisco, CA