If you’re working through an upgrade from SharePoint 2010 to SharePoint 2012, there’s a ton of information on MSDN on how to upgrade your My Sites. I’m not going to go into the specifics, but what I do what to highlight is one particular section of the <a href=”http://technet.microsoft.com/en-us/library/cc262483(v=office.15)”>Overview of the upgrade process to SharePoint 2013</a> post on MSDN.
Let’s look at this particular diagram:
It’s important to note that the above diagram deals with the upgrading to the MySite only, and doesn’t really highlight that upon upgrading the MySite Host, you will also be upgrading the page responsible for rendering the user’s profile.
So what you end up with is a slightly wacky experience whereby the profile page is upgraded to the new 2013 look, but the MySite will remain in 2010 mode until that is upgraded as well.
Summary: You won’t be able to selectively upgrade users and retain the full profile/mysite 2010 experience.