In a Google+ hangout, one of the questions asked to John Mueller of Google was about the change of address tool.
Currently it does not support the ability to move a subdomain to a new domain. The question was asked at 46:57 minutes into the hangout.
My question is regarding change of address tool. Why there is no option to move sub-domain to new domain. What if we want to move a section of our site to new domain or want to move to a new brand?
John answered:
That's a good question, we've been talking about that to the webmaster tools team as well and it's possible we can get an update. Hopefully that will be possible some day.
That would be a nice for Google to support.
Here is the video:
Forum discussion at Google+.