If you watch the developer meeting movie, you get lot of answers.
Yes, it is now Ubuntu based because the focus is on the DE.
And then Ubuntu is easy to use because it support lot of hardware, etc
But in the future it can be based on something else .. maybe arch, or something
But the focus is the DE .. and from login screen to desktop goes in 1 or 2 seconds
Not think KDE or Gnome can beat this.
And I think it pretty rocks