Do you think that the Twelve will eventually become major players in the plot?

[Alberel]

I'm not saying the twelve ain't real. I'm saying that they likely won't appear in a physical form without the Ascian's consent.

I'm not sure where you're getting this idea from. The true Twelve, the original beings, would not have been aether-sucking primals. They were either people, gods or something else. I don't see why the Ascians would necessarily have anything to do with whether they reveal themselves or not.

If they still live then they are still somewhere out there in the world and we may either discover their location or they will reveal themselves when they choose to. The Ascians would not necessarily have anything to do with that. If they are dead, then yes, the only way they would manifest again is as primals but again that would have nothing to do with the Ascians. Louisoix summoned the Twelve to stop Dalamud and that summoning was entirely outside of the Ascians' plan (they wanted Dalamud and Bahamut to simply wreak as much devastation as possible and Louisoix's actions delayed events long enough for the WoL to mount a counter-offensive to destroy Bahamut).