As recently as November 2015, we've had multiple sourcebooks in various stages of announced production.
At that time, my list was:
1 for Edge of the Empire: Mask of the Pirate Queen (Adventure)
2 for Age of Rebellion: Strongholds of Resistance (Location) and Lead by Example (Commander supplement)
3 for Force and Destiny: Chronicles of the Gatekeeper (Adventure), Keeping the Peace (Guardian supplement), and Nexus of Power (Location)
As of now, all 6 of those books have been released, as well as Special Modifications; and we only have one book left in the announced production pipeline; Savage Spirits.
Should this be a source of concern? We still have 1 more EotE, 3 more AoR, and 4 more F&D career supplement books left to "complete" the line; but the lack of new news is starting to make me worry that we've hit the diminishing returns point on RPG supplements and that FFG isn't making as many of them...