Currently i am running ArchLinux (x86_64). Very nice for KSP, i even wrote small bash-scripts for saving and restoring savegames, backup downloaded mods etc. But to be honest, not using Windows was a rather personal descision that had nothing to do with KSP. Therefore, i'm writing this comment, because i do not know if SQUAD really knows how important it is for their business to support Linux. People are following the operating system, not one game only.
By the way: modders should also consider the fact, that there are a quick growing group of Linux users, using their mods.