I know this was asked about a year ago, but I thought I'd update the answer. Hope thats okay. Its just for anyone else who's wondering.
I was asking myself the same question and it is confirmed, Dawn comes to visit Ash in Unova; bringing a glimpse of the outside region's Pokemon, defiantly creating hype in the region. (SPOILERS) And she gets to meet Meloetta!!! Not to mention another subject for the ever-curious Cilan to investigate. ;P
Exciting, right? I'm totally esthetic about it.