Why would the World Government care about one of the Warlords so much? It’s because Moria is the only other person we’ve seen so far who can manipulate corpses.
This idea would fit in with the powers Doflamingo described. The personality-switching operation would allow him to transfer himself to the corpse, and the immortality operation would allow him to live forever as that person.
As we saw when Nami and Sanji switched bodies, strength is indeed determined by the body, not the soul.
She was able to tank hits and commented on how surprisingly little damage she took, while his sky walk did a lot of damage to her body. Thus, a strong body would be a powerful weapon, given that you had some way to utilize it.
Given that the Straw Hat is the marker, what Im is looking at could potentially be the tomb of Gol D. Roger.
It would make sense. The Marines were the ones to execute him, so they would have his body. We know thanks to Moria that bodies can be reanimated, so the Government would likely hold on to the corpse.
There isn’t enough info to say it is for sure the corpse of Gol D. Roger though; it could be anyone who wore the straw hat, maybe someone from the Void Century like Joy Boy. All I’m saying is that it’s the body of someone incredibly powerful.
Let’s look at another thing Doflamingo said in chapter 906.
He says “Isn’t it okay reveal what [the treasure] is? Power degrades quickly… It rots away in no time.” Could it be Doflamingo is dropping us a hint, that the treasure itself rots away in no time? I would venture to say yes.
The thing is, in the freezer where Im is, there isn’t just one of these “tombs”. There’s a light to the center one where the straw hat is, but there are also others.
Perhaps they’ve collected bodies of leaders of the Ancient Kingdom, or various strong pirates throughout the ages. Could the World Government have been amassing an army of strong bodies? Is that why they made Moria a warlord, knowing he would fight on their side of any conflict? Perhaps once they saw Moria was too weak to defend himself, they sent out the order to kill him, not wanting his fruit to fall into the hands of someone else.
Some of you are probably thinking this makes Moria too important to the story, but I don’t think his power is the only one that can control bodies. We already know the Ope Ope no Mi could also be used for a singular body, and I think it’s likely that the Government, maybe even Im himself, has a power to manipulate the bodies. I think Moria was just a loose end also able to control bodies, and they made him a warlord then tried to kill him to tie up the loose end.
Unfortunately for the World Government, it looks like Moria’s powers have fallen into the hands of Blackbeard.
*Theory by Drackend