I wouldn't be opposed to cutting most of the Sand Snakes, but keeping one like Nymeria. I still think Arianne and Oakheart should have been in S4 (with Ellaria as a bit character instead of hiring a great actress for no reason). That way you establish two young characters so they can introduce viewers to Dorne next season. Without, you know, having to shoehorn Jaime there.
Basically: Arianne goes to KL with Oberyn, meets Oakheart, they have a bit of romance (but nothing serious), have various people attempt to propose marriage to Arianne in order to establish that she has been promised to a variety of elderly dying dudes already. Oberyn dies, Cersei decides to send Oakheart to Dorne in order to bolster Myrcella's defense. Arianne is torn between her father's call for peace and her cousin Nymeria's call for revenge. Throw in some intrigue with Oakheart trying to discover the identity of someone who is trying to have Myrcella killed. Arianne seduces him into helping crown Myrcella, in part by convincing him that doing so would save her life. Plot seems to go smoothly until Hotah shows up, heads fly, someone injures Myrcella, etc. And later reveal that Nymeria is the person trying to have Myrcella assassinated. She gets away with it, Arianne is imprisoned, and later Doran reveals his master plan before sending Arianne and Nymeria...wherever they'll go in S6.
Basically follow the book plot but make cuts (most of the Sand Snakes, Darkstar, etc) and add some intrigue. I don't dislike the Sand Snakes, I just don't think most of them need to be in the show. Nymeria will apparently play a big role in TWOW since she's joining the Small Council in Kings Landing, so it makes sense to keep her. But the rest can go.