So, after reading the chapter with the discussion between Doflamingo and the mysterious person, it just hit me and I have come to think that the mysterious person talking to Doflamingo is actually the one and only Dr. Vegapunk.
It would explain why Doflamingo had the pacifistas with him when he was attempting to kill Moria and since he had dealings with the mysterious man who i think is Vegapunk it'd make sense why Doflamingo always had the Pacifistas around him during the war. AND this part is a stretch but also why Kuma was always seen with Doflamingo "early" on in the series
And i don't know about you guys, but I've always assumed that Vegapunk was an old man but wouldn't it be a surprise if this super genius was actually in his 20s-30s like the mysterious man appears to be?
It would appear that this mysterious person is also wearing a labcoat with Doflamingo's fur/feathers on it which would provide a connection between them and their "dealings" and further strengthening this theory and the statement 2 paragraphs above this one
Also, when Doflaming said "no matter how much power you hold with the government, "I'm a pirate you're not my boss" he could've just said high-ranking official if this mysterious person was involved with the military but instead he says this which shows that he's not a military official but also has a lot of power in the WG like say, i dunno, a super genius who works for them and provides unbelievable assets like the pacifistas?
As more information about Vegapunk is revealed, I'll post it here but I strongly believe that this mysterious man shown in this recent chapter is none other than Dr. Vegapunk