In a forum thread on Battle.net, the community manager Nethaera revealed that he will keep us updated with the free name change they talked about a few weeks ago but they do not plan to add more characters which means that the nickname will have a maximum of 12 characters.

Here is what the community manager said about the name change:
We'll make sure to announce the free name change as soon as it's available. We don't plan on it being too much longer though. Unfortunately, I can't give you a more specific time frame as of yet.

Source: Battle.net