Why Yara will appear in Pyke and not in the North

I just want to put this on the record here before we get further into the season. With Gemma Whelan's agency confirming she'll appear in the 5th season in some capacity, we've heard lots of speculation about how Yara will be involved.

The easy conclusion to draw is to go to our book knowledge and conclude that she will be captured by Stannis because well, that's what happens in the books. But there are a number of things that are wrong with that conclusion.

Yara isn't at Deepwood Motte or anywhere else in the North
True that anything is possible but nothing the show has done would indicate that this is the case. While Deepwood Motte certainly exists in show canon and Yara did set up shop there in S2 while Theon occupied Winterfell, she has clearly left and gone back to Pyke as we see at the end of Season 3 when she is with Balon and receives the dick in the box. Furthermore, there has been zero indication on the show that there is any remaining Ironborn presence in the North since Moat Cailin was cleaned out. That scene was very much presented as the Ironborn's last stand in the North and they got routed out. So an assumption that Yara would be in the North at this point seems very unlikely. After her Dreadfort mission, it stands to reason that she returned home to Pyke since that's where she started the mission from.

Yara has given up on Theon
Another theory you could have to unite Yara and Stannis is that Yara will be also trying to attack Winterfell to free Theon and she'll simply run into Stannis or they'll both decide to align or something. However, this assumes that Yara is desperately still trying to rescue Theon. One of the big fan misreadings of the Dreadfort mission last season is that they got so tied up with the "Yara's afraid of dogs, ha ha lame" blanket statement that they failed to note the entire point of the sequence which was to have Yara try and rescue a person who she thought would want to be rescued but to then be completely rebuffed and realize that Theon was simply a husk of his former self and not worth bothering with. The look of disgust she gives him in the kennels before she leaves and her words once she gets back to the boats "He is lost" are clear indicators that she's done with this shit. It's definitely not a "this isn't going to work, we'll have to try a different way another time" sequence, it was a "I was wrong to go on this mission, he's a lost cause." statement. That's not to say she might change her mind later on in the series if/when they run into each other again, but in the short term, that's the show's way of setting her on a new path. In the books, Asha doesn't even know that Theon is still alive and in this kind of condition until she sees him outside of Winterfelll, which is probably an important plot point for the future. The show already had this meeting and realization occur during the Dreadfort raid so they've already got that plot point covered off.

They need Yara in the S6 Ironborn story more than whatever the S6 North story is
Fans would assume that since Asha is captured and with Stannis at this point in the books, that the show would need to get her to that point as well. A couple of things with that theory: in the books, Martin needed to have a POV character alongside Stannis for his march to Winterfell. There were no other characters that he could possibly use so inserting Asha as basically an observer to what he and his army were up to was essential. In TWoW, with Theon's arrival with Stannis, this is no longer the case. We even have the first sample chapter about Stannnis from TWoW be from Theon's POV as opposed to Asha. I think it's a good guess that Asha is not with Stannis longterm and that she has some other adventures to get up to. If that's basically the entire summation of Asha being involved with Stannis, then you could see how D&D might find a way to just skip that altogether and get her to her new destination. Additionally, unlike the books, the show is stuffed to the seams with main characters involved with the Stannis/Bolton collision. We've got Sansa, Brienne and (for now) all the rest of Team Dragonstone present as part of this story who weren't there in the books. Why would you throw Yara in there as well? It seems like overkill.

There's a reason they've held off on Balon's death so long
Contrary to some snarky comments, the show has not "forgotten" about Balon. Have they neglected to mention him for quite a while? Sure. But that's only because the timing for his death hasn't been right. Now that we know Euron is coming in S6, you can see how you'd want to link Balon's death to his arrival as closely as you could which is why it happening in the finale makes sense. With the knowledge that Euron seems to be the only new Greyjoy introduced, it stands to reason that they'd want to have an existing character for him to play off of (this is historically the way they always do big new character intros). So with Yara being in Pyke, recently witnessing or reacting to her father's death makes sense along with having to deal with the arrival of her uncle who conveniently shows up to claim the Throne for himself. Could S6 start with an extremely truncated version of the Kingsmoot (or more likely Yara wanting the throne but Euron saying "no, you're a girl")? Sure. And then we could have Yara playing the kind of role that Vicatarion did as the reluctant lieutenant of Euron who follows him in his mission to attack the reach. I doubt Yara gets sent to Meereen as Victarion did because that ship has sailed (pun intended) but her being by Euron's side in S6 makes more sense from a TV storytelling POV since he's going to need to interact with someone in his scenes and it's far better if it's a character the audience already knows.

So longwinded way of saying I firmly believe that Yara's appearance this season will be in the finale and it will deal with Balon's death (either with her as a witness or simply learning about it). This should set her up for S6 with Euron.