Louisoix’s voice was distant. “Mayhap not. But the Twelve cannot be suffered to set foot upon Eorzean soil.” And then, head bowed, he told her the rest.
No. Minfilia shivered, suddenly feeling weak and cold. She had to fight the urge to rub her arms. “Is there truly no other way?”
“None half as reliable.” He placed a hand on her shoulder. “If I do not return, the others will look to you. You must be prepared to lead them.”
But I am not ready. She turned away, closing her eyes in a bid to stem the tears. “Do they know what you intend?”
“They know enough.”
Minfilia's story makes plain at last that Louisoix definitely did something that no one else knew about beyond just summoning the Twelve, and he didn't expect to return from the attempt. It appears he only confided his true intentions in the antecedent though. I'm assuming this is his trump card that somehow caused Bahamut to vanish.

Hopefully the final account will give us a big tease for whatever the twist at the end of Coil is going to be.

His vehement opposition to a full summoning of the Twelve is interesting as well. Almost sounds like something Gaius would have said...