Don't you guys think that if the blackmail conflict and its resolution is not the main story line, then it would be more interesting to keep who the blackmailer is in a secret? And allow players, even after the end of the story, to identify a circle of suspects and build their conjectures and assumptions? Or would you consider it as an author's betrayal?
I like controversial and open endings, and some mysteries are preferable to remaining mysteries from a drama perspective. But perhaps not in this case?
Aren't you afraid that you won't like the revelation of the blackmailer's identity? For example, because the option was too obvious, or, on the contrary, too unobvious (and all suspicions went wrong), or that you liked the character who turned out to be a blackmailer, or that this character was not in the story at all?