Very out of the left field and EXTREMELY unlikely but: It would be INTERESTING if the Empire "fell" in 5.5/55 and the fallout of that became the driving plot of 6.0. Esentially diving into a Civil War between the Optimates and the Populares. Said instability would allow us to explore Ilsabard, since the conquered nations would use the opportunity to liberate themselves (hopefully offscreen, so as to not rehash Stormblood's plot and fuel a "everyone is useless without the WoL" thing).

I'd GUESS the cause would be our very public defeat of Zenos (AGAIN, and hopefully for good), leading Fandaniel to lead the Optimates in the ensuing chaos, with Maxima FINALLY getting something to do as he rejoins the Populares (and, perhaps, rebuild the Empire as the Garlean Alliance, letting the nations that actually flourished under Garlean rule rejoind under their own rules).