I still don't get the Dorne plot moving forward. People keep saying they saved the plot with the Myrcella stuff. But now, Doran lost his future daughter in law, one who could've been a major power or heir to Casterly Rock, his only heir (in the show) is now in Lannister hands and the second chance he gave Ellaria seems to have backfired. Even in the books it didn't make much sense, but it's completely balls up in the show. So much for the 'we don't hurt little girls in Dorne'.
Unless Myrcella death is used as plot device for Jaime to move onto Riverlands or into Brienne arms or whatever. Maybe Jaime now becomes the character he was in books. Realizes he has no one who really loves him, he wasn't a father to his own children, he's nothing without his hand, there are no accolades in his white book for him, etc.
I guess that since almost all of the characters related to Dorne from the books aren't present, nor are most of the plot threads, the writers of the show figured it made more sense to have Ellaria try to start a war by murdering Mrycella and leaving the prince in Jaime's hands. Presumably she figures Cersei will kill or torture him, provoking war with Dorne.
That's my guess. The plots now diverge so wildly I don't know what to think. I know the entire GoT Dorne storyline has been awkward and boring to me.