I think it was in one of their recent interviews, i am not sure, I keep seeing it stated on the forums.
I'd be really interested in seeing that interview if anybody could point me in the right direction. The above comment just made me notice that I had been taking comments about story being deprioritized for granted, and that after having spent the past few days catching up on dev news I hadn't actually seen anyone official say anything about that. I just spent like fifteen minutes doing searches on all of the TOR and general gaming blogs, and none of them really had anything recent about changes to story development that I could find. Honestly, the only thing close to a source for this seems to be comments on this forum from around June that had people asking if the increased priority of legacy content would mean story delays.
On the main thread topic; Personally, I don't think we'll see an Act 4 until there is a full expansion.