I definitely think the Tython and Korriban FPs and the start of a new storyline (especially one that kicks off by attacking the other faction directly) is enough to keep a significant number of players sticking around who might otherwise have jumped ship.
PvE players have been in wait-and-see mode since late November 2013. You think two 'tactical' FP's is enough to keep them around for another 5-6 months? On speculation that the next storyline is all that? Even if they throw in another two between now and 3.0, that's a pretty hard sell.
My guild is moving on and me with them. Will we come back for 3.0? Hard to tell. Not only is it going to depend on the new content, it's going to depend on the next game failing hard. The dry spell is going to cost them subs, whether or not that'll be statistically significant is something I can't answer authoritatively
It's a matter of cadence. It is not enough to committing to pushing out releases on a regular schedule, what you release is equally important. I understand the idea behind staging features, but making those consecutive update cycles GSF exclusive was such a phenomenally bad idea. And then to only release GSF with one mode and two near identical maps... I can't be the only person to burn out on that.
New OPs, FPs, PvP and GSF maps have to come out on regular basis with an appropriate frequency. Once a year doesn't cut it (Don't care what WoW thinks, it's still dumb).