Betrayal from an unlikely quarter; theories.
When the vial was revealed to be damning evidence against us, my heart fell. Momodi was quite specific about keeping it on our person - something we would have discarded as irrelevant otherwise. As it wasn't addressed at this point, I'm presuming her betrayal will be addressed in 3.0.
#DarksteelFoilHat
Unless it's a double-bluff that Momodi and Lolorito are in on (and Kan-E-Senna/Merlwyb as Blaon highlighted above). Nanamo states she wishes to abdicate and then does so in a very subtle way. I'm pretty sure Teledji was innocent of arranging it; he seemed sincere in his denial when he didn't need to be - it was the mysterious handmaiden (shown to be in the service of Lolorito) who alerted him to the 'poisoning' after all. We were to take the fall and be imprisoned/rescued to get us out of the public eye too.
However, Nanamo didn't anticipate Raubahn losing it, killing Teledji and himself being mutilated (I'm fully expecting Raubahn to get a Garlond Ironworks arm upgrade early on in Heavensward). Perhaps she wasn't aware of issues within the Crystal Braves which came to a head as part of a separate plan by Teledji. It would explain why the other GC leaders bricked it and left.
If all this were the case, Nanamo's abdication would be less a dereliction of duties and more about going undercover to solve an issue that was plaguing her deeply that she couldn't do as Sultana. Presumably something to do with Omega Weapon? Though tbf I'm not sure on that, having completely ignored Frontlines so far.
Also, Yda will return in 3.0 and 'finally' get a new mask from Rowena. That cutscene will be cheesy as hell.