Marcei,
I am in general agreement in your brief post. I think it also relevant to the behavior of a material particle in motion without referring to an external field effect. Simplifying... the leading edge of a particle volume dense enough to be inelastic, would not be in/at the same moment in its own volumetric bounds as that of the trailing edge. Any motion could be considered absolute in this respect of self referral because physically the motion would cause the energy at material density to 'smudge, altering its density as a result. Theoretically (as distinct from observationally) we might be able to ascertain a real, absolute value for a particle in motion by predicting a density difference and a real physical contraction both fore and aft along the axis of motion as a coefficient of light velocity; flattening a spherical rest volume to a shape of e prolate spheroid with an attendant expansion laterally perpendicular to the axis of motion.
SR2.0 so to speak. We would still have Lorentz Invariant measurement in any observation, but the causal effect of the reduced density of the particle in motion would be what is observed. Perhaps this could help explain the wave characteristics of EMR which would interact en passant of an external field, while the ballistic characteristic observed in the photo-electric effect would be a capture or collision event which would actually stop the motion of the particulate mass and restore its rest density in the energy exchange. best jrc