Dear David,
I've read through Israel Perez's essay, but the concept of a material medium doesn't seem to be able to produce the dimensional curvature of spacetime effect described by general relativity - only an energy field that can impart kinetic motion to matter seems able to so.
I can't precisely describe the mechanism that might be involved, but it seems intuitively natural that the localized aggregation of the potential energy of mass would produce the complementary effect of locally contracting surrounding space-energy. Like the localization of potential mass, the contracted space-energy (energeum) would be directed to the focal point of contraction.
It would be the energy gradient produced by energeum contraction that produces the directional accelerating effect of gravitation. IMO, Einstein's 'light moving in a straight line through curved space' was a description necessary to convince astronomers to test his eclipse predictions, since they could not consider that light could be curved! I see this more as the propagation of light waves being temporarily tangentally redirected as it traverses a (radial) field of directional space-energy in the proximity of a sufficiently massive object.
Well, I don't want to beat a dead horse, but I think only energy within space could contribute to the effect of gravitation - no material medium density could cause the motion produced by gravitation.
If the manifestation of virtual particles, as I think can be measured by matter-antimatter annihilations, is in turn a measure of spatial energy content, or density, then I would expect that a gravitational gradient field of condensed space would produce varying rates of virtual particle-antiparticle annihilations. If the virtual annihilation rate did vary with gravitational effects and this relation could not be explained in any other way, it might offer physical evidence of energeum! At least, that's my thinking...
I'm not capable of pursuing these ideas, so if they seem to you to have any potential I would hope that you might be able to further pursue them. I'd certainly be glad to help in any way I can.
Obviously I do find that your conception of energeum dovetails quite nicely with my thinking about gravitation - I have also thought that if universal expansion were accelerating it would also require the action of kinetic space-energy. Moreover, I suspect that the existence of energeum is necessary for even the initial expansion of the universe; that the primordial energy that was not converted to condensed matter would have filled space. This fundamental, omni-directed energeum might be evidenced by the dispersal of gases in space...
Conversely, like dark matter, I'm actually highly skeptical that the acceleration of spacetime expansion and dark energy was properly inferred, depending as it does on the constant peak emission luminosity of type Ia supernovae produced by accreting matter onto a white dwarf until it reaches the Chandrasekhar limit - recently found to be more often than expected produced instead by the merger of white dwarfs of varying masses. But that's another discussion...
Frankly, I'm much more excited about the potential for energeum in the production of gravitational effects. If my thoughts about a test measurement have any validity, it would certainly be more feasible to evaluate...
Sorry to ramble on - I have been thinking for some time that some form of kinetic space energy was necessary for the physical production of gravtational effects. I really appreciate any further consideration you might be able to give to the subject.
Sincerely, Jim