There is indeed pretty intense speculation that they're going to cut it. One of the directors and the respective actor were like, "I dunno it's pretty ehhhh for us doesn't seem too important." I'd take issue with that, but I'm holding out hope they'll open next season with it.
The only other reason I can think of is because so much shit happened in S4 already, and the next couple books aren't that action packed. Mostly Cersei, Dany, and Jon doing things. They hopefully just want to open S5 with a huge twist so it doesn't seem like a dull follow up.