Is it an actual install or a full game cache?
The original xbox had 3 750mb partitions that it used for caching games in the backgroung. I remember Ninja Gaiden Black load times were horrible when you first put the disc in but were much faster when I had done it's copying. The game stayed in the cache until you played something else, even if powered off.
This could be an evolution of that method. Put in the Halo 5 disc, 720 starts to cache as soon as it's launched until it's entirely stored on the HDD. It will stay there and load direct next time while checking the ODD to make sure you still own it. Start playing Destiny and it deletes the Halo 5 cache and starts the Destiny install. Rinse and repeat ad infinitum and it only needs 50gb of space.
