c is calculable
It's widely understood that relativity claims that c is a constant, or put another way, the axiom holds that there exists a velocity that is constant in all reference frames: thus 'exceeding' the speed of light (at least for objects with mass (or in the case of photons, with momentum) is not so much impossible, but meaningless. Like 'biting your teeth', or 'measuring' the position and velocity of an electron simultaneously.
What isn't widely known is that the speed of light can be derived from first principles, and had been from the 19th century, from the permittivity and permeability properties of the vacuum.
Since the vacuum is reasonably supposed to be invariant itself, permittivity and permeability should be fixed and so the value of c (in vacuo). But suppose during the earliest periods of the space-time expansion, those two properties were somehow... what?... concentrated? Velocity of a wave in a classical 'medium' is a function of its restoring-force, and if the restoring force is somewhat 'enhanced' by the 'concentration' of the two properties, and excusing my single-quotes, then perhaps the value of c might have been greater in the earliest universe.
Also excuse my calling the spacio-temporal manifold a 'medium', but it seems a fundamental universal in classical, relativistic, and quantum domains is the oscillatory phenomenon required by Newton's classical dynamic of displacement and restoring force.