I'm still skeptical that we know enough to absolutely positively rule out FTL, but I will say this. If you think deeply on it, a universe with FTL is pretty weird. In some respects it would be identical to time or dimensional travel. It would imply that causality is strange or many worlds is literally true or that space time is fragmented or something equally wacky. It would also transform the Fermi paradox from an interesting question into a silently ominous mystery like a minor but devastating early plot point in a good horror flick.
But hey, when we discovered QM the weirdness of the universe went up a notch. As a general principle we can set a hard lower bound for weirdness but not an upper bound.