Regarding air pressure (suction), a reed organ plays it's reeds on a mere
breath of air.  A piano pneumatic requires a greater amount of kinetic
energy.

Reed organs use low pressure of higher volume, whereas piano pneumatics use
high pressure at lower volume.  The difference is in a) the kinetic energy of
the air, and b) the volume of air being moved.  To what may we compare?  A
reed organ is like a man who eats many small meals throughout the day.  A
player piano is like a man who eats big meals but less frequently.

Consider the mass of the little brass tongue in an organ reed, compared to
the mass (not weight!) of a piano action.  Vacuum first has to overcome
inertia to set reed or hammer in motion; the more mass, the more kinetic
energy (higher pressure/vacuum) required.  Also, the tongue vs. hammer are
doing 2 very different things.  The tongue is merely vibrating.  The hammer
has to travel and strike with significant force.

It might seem that the same vacuum reservoir would serve both purposes, if
it's on the high vacuum required for pneumatics.  Let me inform you, before
you make an irreversible mistake.  The organ reeds will likely ruin because
they (being "free" reeds) have nothing to rest against if overblown.  The
result is that the force of wind can bend them over.  Or they may just break
off!