Howling:10 or 10A?

Everyone seems so determined to figure out the role of John Hurt's Doctor in the 50th that no one is thinking about David Tennant. What role will he play? Everyone assumes he's going to play the 10th Doctor, but from when? Rose will be there, so is it 10 with Rose? Meaning before he ever met Donna or Martha? Before he lost Rose in Doomsday? Before he ever met the Cult of Skaro? He was a different 10 back then; a very different 10. The loses hadn't piled up yet. Or, since Rose is there, will he be playing the meta-crisis 10? In a supposedly multi-Doctor 50th Anniversary, one real Doctor alongside one as-of-yet unexplained guy and one mere duplicate would almost be a waste; might as well just substitute 11 with his Ganger, too. Or, maybe, will Tennant be playing both 10 and meta-crisis 10? Thoughts?