'Timo' wrote,

(a) aberration: if two mutually-gravitating bodies are moving (through
the
background of waves/energies/particles,
why is the force on each body directed
towards the other?

To preface this, let the Plenum of space be under a state of extreme
hydrodynamic pressure. This is key to understnding flow sinks and the
mechanism of flowing-space gravity.

OK, short answer: each body is an omnidirectional *flow
sink*. The *speed of gravitational charge* (NOT velocity of spaceflow)
is instantaneous, hence no aberration.

Long answer: Let's change the scenario slightly to the Sun and its
family of planets. The Sun is an omnidirectional flow sink, its Flow
Field (aka its gravity well) extending well out beyond the orbit of
Pluto. The *speed of gravitational charge* (again, NOT velocity of
spaceflow) is instantaneous at any level in the Flow Field. This common
instantaneity at every level causes the spaceflow to intersect each
planet's orbit with *no aberration*.

(b) Drag. Should bodies moving through
the background experience a drag force?

No, not unless they move into relativistic speed regimes. At
subrelativistic speeds, space exhibits frictionless-ness or
superfluidity ('hyperfluidity'). Spaceflow through the body's atomic
lattice is frictionless. This property of space underlies conservation
of momentum.

Should the effects be observable?

At subrelativistic speeds, space exhibits "viscous-ness" or inertia
_only_ to an object's acceleration. The now-accelerating spaceflow
through the atomic lattice imposes a force upon each atom in the
direction of flow, creating resistance and thus the inertia of the whole
object against acceleration.
The inverse occurs in a gravity well; the accelerating
spaceflow through the atomic lattice now imparts momentum to the object.
The object takes on the acceleration of the spaceflow. This is the cause
of gravitation.

To which I might add the other things
that should be explained by an
explanation of gravity:

(c) Why is inertial mass equal to
gravitational mass?

Spaceflow through the object's atomic lattice imposes a 'tensioning' or
stretch force to each atom along the axis of flow **whether the object
is being acceletated through space or accelerating space is flowing
through the object** (see above). Exactly the same property of space,
and exactly the same mechanism is at work in both cases. This is the
mechanism of gravity-acceleration equivalence (or equivalence of
gravitational and inertial mass).

(d) Gravitational time dilation.

The deeper you go in a gravity well, the less dense the spatial medium
becomes as it accelerates toward the flow sink (the gravitator is the
'venturi' to the highly pressurized spaceflow). In less-dense space, the
clock runs slower (Pound-Rebka et al.) The speed of light is also lower,
locally (GR's first observation superceding SR's invariant speed of
light).
GR could only *describe* the effect. It could not _explain the cause_
since there was deemed to be 'no medium'.