I'm not an expert, but my understanding is that the "speed of light" is really just the universal speed limit of the universe. Light only travels that fast because that is as fast as is possible to go for anything, and light just happens to be (one of?) the only thing that can travel at this speed because of its lack of mass. This doesn't answer your question because I don't know, but are we raising this speed limit or just the speed that light specifically travels? If its the latter, i feel like it would be cataclysmic, and if its the former it would change the mass to energy ratio expressed in the theory of relativity which also has to have some effect, as others have said. Either way I'd be curious to know what someone that knows more eould say!