The Knot in Meereen is already settled, right? (spoilers extended)
I just re-read ADWD, and I think GRRM has pretty much prepared the solution for Meereen, right? So it shouldn't be hard for him to advance to Westeros in the next book.
Yunkai is pretty much defeated already, they just didn't know it.
Ser Barristan is leading the Unsullied and the main forces to hit Yunkai directly.
And then Victarion is there attacking their flanks (causing panic)
Tyrion is luring the Second Sons to betray Yunkai.
The Harpy is most likely Green Grace, as many readers suspect. Hizdahr is just a pawn. (Wouldn't it be interesting if Pretty Meris dealt with her?)
And then Daenerys will make her glorious return, spurn Victarion, and go back to the West with Tyrion and Barristan.
I hope Ser Barristan will survive. I don't like the TV series adaptation 😞