User blog comment:FairyRaven/Fairy Tail Chapter 437: Magnolia, Review and Commentary/@comment-24546844-20150525170715/@comment-9595671-20150525223153

Mashima said the Sun Village Arc was the halfway point, so I'm assuming that we're far from an arc where the two finally become the enemy. They could influence the next few villains, but I don't think that they'll directly do anything for the time being.

I mean Zeref seems to imply Acnologia might be a bit lazy because he wants a real opponent despite he could rule the world if he wanted. (which seemed to have happened in Future Rogue's time) So until more villains get thwarted I don't think he'll be interested in acting just yet.

Also is it just me, or does it seem like Mashima doesn't like changing how most of the more prominent characters look? Usually when a character looks gets a new appearance it seems like its one of the more minor or semi-prominent characters.