That's decent evidence. More evidence for it happening than Cleganebowl.

Lesley Goldberg
‏@Snoodit
New S5 cast members include Keisha Castle-Hughes, who earned an Oscar nomination for her starring role in Whale Rider. #GOT #SDCC

Okay, so the official press release states that this is just SOME of the new cast, and in previous years they haven't announced it all at once. So there's still hope for the Greyjoys. But, it lists Trystane as the heir to Dorne, which means...
Arianne is cut.
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To be fair, it's probably one of the few characters you can cut right now that absolutely has sexist connotations at least. The whole Dorne subplot revolves around how the eldest child inherits and the notion that women are far more equal. Cutting the female character that is the heir to Dorne and the representative of these themes smacks of something uncomfortable, however unintended.Let's call D&D sexist! :b
Not just Victarion, Euron too. Euron who has been touted as Dany's endgame villain for a while now.
But these cuts aren't indicative of the book IMO. D&D did recently say that henceforth the show is the show and the books are the books, with only a basic blueprint to connect them.