Samsung may not name its next flagship phone as S4. If you are waiting for S4; it is most probably that you will end up not getting the handset named S4.
SSSS......Superstitious Samsung ?
The pronunciation of 4 is not that much cool in the part of the world from where Samsung comes from. In Korean, it implies kill; and in Chinese and Japanese language this implies death. The samsung might not take the risk of naming it as S4 and more rightly because of the fact that none of its previous models are named with 4.
Unbreakable glass : The next big thing
Samsung might be thinking of unbreakable glass in its next devices. And with this new thing, you might well have a new series name. Samsung might also continue to name it as galaxy 4 and hoping that the new device would make a killing in the cut throat smartphone competition.