In the upcoming M15 release, it has been hinted that Avatars of the planes themselves exist. Perhaps Nicol wishes to manipulate Ravnica's in some way?

[img]http://s3.gatheringmagic.com.s3.amazonaws.com/images/sets/M15/Soul%20of%20Ravnica.png[/img]

It would certainly make a switch to other planes in terms of plot more viable.