Also another possible hint that GRRM has planned for something anew and good grows out of the destruction of Slaver's Bay is the Pale Mare, which could be a possible historical connection to the Black Death.
The Black Death for all it terribleness changed our world forever and actually despite the countless deaths it inflicted had positive outcomes - mostly is signalled the beginning of the end for feudalism in Europe, the peasantry due to their lesser numbers had more power over their overlords than they ever had previously. Lesser peasants mean a higher market demand for peasantry work, so peasants could demand more for their work or they could leave and go to someone willing to offer their demands.
With the Pale Mare basically wiping our Astapor, the Yunkai sieging suffering it, I think some people in Meereen are dying from it (not too sure, cant remember), Yunkai could be plagued with it for all we know, Dany could have the pale mare as well. The population of Slaver's Bay is going to decreased substantially, perhaps even more than 50%. If Dany's forces win the siege of Meereen and crush the slaver forces, no more slaves will be brought in.
That automatically gives the lower classes more power
The decreased population food won't be such a problem as it once was.
If Yunkai is infected, they could be totally exhausted and depending on the pop size, the conquered Yunkish could actually be moved to Meereen to keep everyone in 1 city.
All of Meereen city state enemy armies have been destroyed by arms and disease, and won't be threatening the new free state any time soon
Braavos, Volantis (soon) and (possibly) Pentos could possibly support the new free city of Meereen with trade.
Astapor and Yunkai could be repopulated in time as free cities
So Dany might not even have to control 3 cities, just the one. One city can be manageable IF she knows who to put in charge of Meereen in her stead.
The Pale Mare for all the death it has inflicted and Dany's ideological intervention, could lay the seed for a new free Ghiscari nation. The Pale Mare is key to change. The night is always darkest before the dawn so to speak.
Also could Greyscale have the same affect on Westeros that the Pale Mare has in Slaver's Bay. Could Greyscale cause change in Westeros? Lots of smallfolk have died already.
Butterbumps. Dany's purpose in this series is to be an agent of change, and I agree that the brightest, hottest embers in a fire die out the quickest will probably apply to her. She is already changing Essos, probably forever. But her path will ultimately lead her to Westeros - what change will/can she bring about in that feudal system? Gender equality? More powers for the peasantry? A Charter of Rights, a Magnus Carta if you will?
If her purpose is an agent of change, she simply can't be a heroine that swoops in saves the day from the others and restore the old feudal system. What is her purpose regarding change when it comes to Westeros do you think? And who is likely to carry out her changes when she will (probably) die?
It will be cool if that shadow of a dragon over kings landing is a dream sequence of Dany's (or other). They see a shadow of a dragon over King's Landing, but no dragon - just a shadow. Foretelling the arrival of (F)Aegon.
It is also amusing to see some posters here get a stiffy over the possibility of Dany losing fans this season. Hehehe.