Superluminal preons (superbradyons) with a critical speed in vacuum much larger than the speed of light would, if they exist, play a fundamental role as constituents of the physical vacuum and of the conventional particles considered in standard theories. Then, standard Lorentz symmetry and quantum mechanics would not be ultimate fundamental properties of space-time and matter. If superbradyons are present as free particles in our Universe, they are expected to couple very weakly to "ordinary" matter, but they can spontaneously decay by emitting standard particles until they reach a speed equal or close to that of light. They would then form a cosmological sea where the relation between inertial and gravitational masses would differ from conventional Physics. Superbradyons may be at the origin of cosmological and astrophysical phenomena usually associated to dark matter, dark energy and inflation. They can also be a source of conventional cosmic rays of all energies. In such a scenario, superbradyon spontaneous decays and similar interactions would be candidates to explain data on electron and positron abundances (PAMELA, ATIC, Fermi LAT, HESS, PPB-BETS) considered as possible dark matter signatures. Superbradyons emitting this radiation may even have comparatively small inertial masses, and kinetic energies not far away from those of the decay events. But in most cases, such "light" superbradyons could not be found at accelerator experiments. We comment on several basic physics and phenomenological issues in connection with the superbradyon hypothesis.