Bosnia has always been a separate cultural identity. I seem to recall the 1908 crisis when Austria-Hungary annexed it from the Turkish Empire. It was never politically in Serbia's sphere until 1917.
Having said that, this is a stupid move by the Bosnians, who should realize their real allies are the United States, not a group of opportunists who will sell them out when the going gets tough.
Actually no, Bosnia has never had its own cultural identity, Bosnians are either Serbs or Croats who were converted to Islam. Many Bosnian Muslims still retain certain Serbian Orthodox religious traditions that revered Christian Saints (slava).
Bosnia was Tito's bastard child social experiment, he pushed it off as a unique ethnic and cultural identity when it is not.