Here's a couple relevant WoB's, with the most relevant one at the end:
And in Chapter 23 of The Bands of Mourning, it says that the statue in front of the Sovereign's Temple is a statue of the Sovereign.
The statue is of Kelsier. The statue is of the Sovereign. Thus, Kelsier is the Sovereign.
We know it's not Spook's body, and we know there are numerous scars on the forearms, similar to Kelsier's original body. Beyond that, it's pretty much guesswork. We probably won't know for sure what's going on there until we get a Secret History 2.
Edit: Ninja'd!
Zath's post in Do we know who The Sovereign actually is? was marked as the answer