Also something to support your theory of him being Vegapunk, reason why he gave the order to kill Moria. Maybe Moria is his pacifist weakness? We know he made from bodies so if Moria implants a shadow in it he can easily take it over.
I still don't think it's him though and here is a good assumption to help support your theory enjoy it. (Not mine some one elses, still doesn't change my mind.)
Well in the chapter Doflamingo does categorically state two important points about the mystery person:
- That the person holds a very special position of importance in the Marines
- That the person regardless of the said importance has no official authority over Doflamingo
Now we take these two into context with the fact that to our knowledge there is very little between Sengoku and the Gorouseii in terms of authority other than Kong. While its not unrealistic, it is a bit ...inefficient to put someone else in that middle ground.
We already know that Gorouseii are, short of maybe the Tenryuubitto and possibly a King / Emperor figure (far fetched), the highest authority on the planet. So if its not anyone of these people that we have seen, and Doflamingo specifically makes the statement about authority, who else could it be?
While I'm not saying that it IS Vegapunk with certainty, the pieces do seem to fit together. Lets examine what we know about Vegapunk:
- He is a genius scientist whose inventions have basically allowed the Marines to become the force they are today. Think about everything he has created, the Pacifista + Kuma, Devil Fruit research, not to mention what could be an endless array of deadly weapons. With this in mind its not hard to imagine that such a man would hold tremendous influence in the Marine hierarchy, even if he might not hold any official authority or title.
- The fact that he has someone like Sentoumaru to protect him and his lab shows how much the Marines value him, not to mention the supposed reaction to Franky's blowing up his old home.
So now we come to why someone like Vegapunk would be ordering Doflamingo around. This is where it becomes tricky as we know nothing about Vegapunk as a person other than the fact that he has to potential to be a stereotypical Mad Scientist / Evil Genius.
What we do know is that Doflamingo is a power hungry and ruthless character with bold ambitions and no set reason to be loyal to the Marines. Yes he followed orders during the War and its Aftermath but from his behavior and his actions its clear he did it more because he enjoys violence and chaos and it suits his ends. His conversation with the mystery person only reinforces this point, he categorically states that he would simply walk away if he the job wasn't "interesting".
The reason Vegapunk and Doflamingo would work together could be simple; Vegapunk might have nasty ambitions of his own and may have teamed up with DoFla with the promise of giving him the means to achieve his ends in exchange for cooperation. This could mean anything, heck Vegapunk might secretly give DoFla use of Pacifista units to do his dirty work. In the end DoFla can have his New Age and Vegapunk can do whatever he has planned.
I admit almost everything in the last part is wild speculation but the examination of facts may ultimately point to this conclusion eventually.
But then again, this is One Piece. Not one of us on this forum would be here if it was anything but unpredictable.
Heck the mystery person might even be a girl..notice the weird hair / shadows under the bowler hat......BTW who the heck wears a bowler hat anymore???