The early Ubuntu TV work was using Unity 2D as the basis for its interface, but now it must be ported to the standard Unity code-base with Compiz. While hopefully the performance won't be too bad for Unity on Ubuntu TV, it's a large undertaking.
In the latest Ubuntu TV weekly update, the status of the Unity porting for the TV version was shared. Changing out Unity for Ubuntu TV is just over half-way complete. "Since Unity 2D is deprecated for Ubuntu 12.10, much work is being done to port Ubuntu TV to Unity 3D. Much of this work is included in the 12.10 Ubuntu desktop. Currently the transition is approximately 60% complete."
Additionally, "For TV’s Unity, launchers no longer track the status of applications, nor will the associated lenses be loaded."
Dropping Unity 2D also caused big problems for the Ubuntu desktop on ARM hardware.
We should find out more about the Ubuntu TV plans later this month in Copenhagen.