I quite love the show, but this sort of thing is always fun. Here are my ideas for Season 5 & 6:
Cersei convinces Jaime to go to Dorne to rescue Myrcella from a 'threat'; however it was faked by her to manipulate Jaime. Arriane tries to have Myrcella crowned like in the books, but both Jaime and Doran converge on her and Myrcella is killed by accident. Jaime and Arriane are imprisoned and Doran reveals how all this was caused by Cersei's bad planning, sowing distrust. Secretly he tells Arriane the fire and blood speech and his support for Dany. comes to pick Jaime up and urges him to do his duty and go to the Riverlands to gain peace and moves away from Cersei's madness when Brienne comes like in the show.
Cersei is the same but more paranoia about Tyrion etc. Tyrion and Dany's story would be the same but have him and Dany play Cyvasse when they first meet and introduce Moqorro on his journey. Possibly have the siege last the whole season and end upon Dany's return.
Euron wins the Kingsmoot in Season 5 because of his dragonbinder horn. Yara mistrusts his mad magic ways and convinces half the fleet to join her in betraying him for Dany while he is distracted raiding Westeros like Victarion in the books. Theon would still join her though at the start of Season 6, and on the way they meet Moqorro and maybe Jorah?
Arya goes blind halfway through season five, regains it via warging. Lady Crane is acrually her teacher for my Faceless Man training, but when she sees Meryn Trant she becomes Arya again - cue the Waif chase/fight, then she disguises herself as the waif and joins the players in going to Westeros.
Jon is the same, but Sam leaves at the start of Season 5 so we can have more time in Old Town and learn about magic and dragons. Likewise Brans is the same too. Sansa meanwhile goes to Winterfell as Alayne Stone in order to rally the Northern Lords against the Frey/Boltons. Only one of them recognises her - Wyman Manderly who reveals that he knows where her brother is. However, he is beaten to getting Rickon by the Karstarks/Umbers cus Jons actions. She sends a letter to Jon prompting ftw. The rest is the same as the show, but a bit quicker because Sansa has already gained northern support etc.
Dunno, the show is probably better than what I have got.