>>105394081) lightspeed as a fundamental limit is a misnomer. It's the speed of action that is limited. Actually, if you use rapidity instead of velocity all these counter-intuitive things disappear and it can become infinite.
2) light having mass will change everything. It would mean that electromagnetic force has finite reach. Atoms would fall apart.
Light is always as fast as light, there's no slowing down in media or anything. You just perceive it as that since the phase velocity changes due to interactions in the medium, but the group velocity always stays the same.
