[@Winston Smith] Another fandom theory is that that dragon is Sheepstealer. 

[@Abefroeman] I will say that the fate of Sheepstealer/Nettles, and Cannibal will actually be expanded on further in the story and have pretty sizable implications on the plot. If someone wants to know more to possibly build a sheet using those characters as part of the background, everyone's free to PM me. 

As for the mystery eggs, I would assume the majority of them were found in the ruins of Summerhall, and are being kept close at hand. However, I would think it's possible that the Essosi nobility, especially those who have blood ties to Valyria might have an egg as an heirloom and there could be some in Asshai.