Now I know what you're thinking, Elixir - You hated the spy and how much it destroyed the meta why are you even considering this option?
Spy was garbage because it ended up being a self confirmable town and most of the town are the ones using pms anyway. Spy is still a bad role as it disincentives strategic play by evils (and I think the upcoming Party Host does a way better job being an offset counter to that as it is limited in scope.)
Now enter the current meta which is HeLlO Im MaYoR pM mE pLs which is starting to get equally as swingy having the entire game decided by one person without real interaction. Giving the PM reading ability to consig gives the evils a threat in that they might get an entire role list given to them allowing them to plan their hitlist accordingly (of course they could be reading lies). After the investigator rework, unless exact role is turned on the consig isnt exactly a powerhouse of a role right now and doesnt get a lot of meaningful information. Rather than make another role like snitch I'd rather power up the roles that currently aren't super strong (again, unless you activate the turbo consig which is probably busted).
I might be missing something but if consig is the only role that can read them all they're not exactly going to admit to it - and because spies can't do it the town wont turbo lynch a spy thinking they're a consig.
Just a shower thought idea - how do we feel about it