The empire and republic are at war, they don't have to know that the Zakuul are coming. We all know that FE starts with your character waking up from a 5 year carbonite freeze, I assume that this happens after a major battle. I don't want to know prior to FE as to why I was put in freeze but we can have a major event with like for example, never ending waves of Zakuul forces attacks, were republic and empire indirectly fight side by side... or have them individually on Dromund Kass and Coruscant.
By no means is my idea necessary, but let's face it, once FE is going to come out, populations on servers for the 1-60 are going to be close to none with the ability to start a new toon at level 60 no one is going to play the old content since the back story so far will be irrelevant to FE.