You will of course note that faction 3 in X-Wing happened after six waves of content.
For Armada, the Rebels and Imperials need to have a solidified presence before a third faction can be considered. By the time they're being thought up, Imperial Star Destroyers and Mon calamari cruisers should have been released, along with the popular capital ships, to bring balance to the game with two distinct factions. Then once they're firmly in place, throw the game off with a third faction.
I myself don't care at all for the Zann faction. The Galactic Civil war is about the Empire and the Rebellion having at it- no notable third party was strong enough to make its presence felt. If faction 3 gets anything I don't think I'd be satisfied with anything over the size of the Victory.


