Humor me for a minute. After thinking about the turaga story on how Mata Nui was put to sleep by his brother Makuta, and watching the MoL trailer I've come up with a startiling hypothesis. Seeing that makuta always seems to have a body simular to the residents of Mata Nui(such as the matoran body in the online game, and the toa body seen in the movie trailer) couldn't Mata Nui have one too. Now with this in mind let me show you more evidence!
When you watch the trailer you see that the mask of light was hidden in a bolder, and begins to glow when it is released in the lava. What if Mata Nui's spirit was inprisond in the mask of light while he was set in his eternal sleep. Now with the mask being found his spirit can be released and make a seperate body (takunuva) to help the toa protect his island while he recovers from his long sleep.
So, what do you think? Could I be on to something here, or really far off?