Aerys doesn’t appear in the main story, but as with all of the side stories and history books, Martin is planting things in the past that relate to the present as parallels, rhymes, dramatic ironies and foreshadowing.
Aerys’s story is loaded with parallels and rhymes to Daenerys’s story. Like with Dany, people thought Aerys was going to be a good king. His rule seemed promising in the beginning. His friends said that people would know him as Aerys the Wise or Aerys the Great.
Like Aerys, Dany lost a son, was betrayed by her closest friend, and is haunted by prophecy. I suspect Dany’s time with the Dothraki in TWOW is going to be a sort of kidnapping to parallel Aerys’s kidnapping at Duskendale, marked by a change in attitude in each case.