Question about ASP.NET Identity

Hi,

I'm playing with the new Visual Studio 2013 and One ASP.NET. I'm confused about something:

The new User model seems to inherit from IUser where the Id property is defined as a string type even though its values seem to be GUID. It seems in the database, it's defined as an NVARCHAR field. Any idea why? What's the advantage of defining a GUID type as string? Any idea why ASP.NET team took this approach?

I wanted to change the data type to GUID but looks like there are a lot of dependencies and was not able to change it.