It wouldn't matter anyway..
Whether or not the speed of light is, was, or will be faster or slower than it is "now", it's kind of like saying time passes slower or faster than it used to--from our perspective, within the system, it's consistent, however much the universe's expansion is accelerating. Kind of like if you were an AI and someone kept changing the clock speed of the system you were running on--without anything external to observe, you'd never know.
It's great that someone devised a brilliant experiment to test this, but I always look at these things from a perspective of "can this be exploited for something cool?" such as FTL or time travel. Unfortunately for now it still appears that you can't win, can't cheat, and can't quit the game. (unless you die)