TumblrFrostbite's AU Questions: Would Maria Hill had been a member of that group if she found out that they reformed? For that matter, would she black mail them into letting be a part of their little secret clubhouse and make some demands and/or changes to how they'll operate too?
Maria would not want to be a part of the Illuminati, because she would see it for what it is and immediately be opposed to the idea. Once they all insisted -which they totally would- she’d have no choice but to stay there and threaten the rest of them with exposure if they were against her involvement. She’d be forced into the position of being the voice of reason, and it would not be enough. The Illuminati group would still go down dark pathways, and Maria Hill would then be a party to those mistakes, no matter how much she tried to argue against each of their bad ideas.
It’s pretty telling that the first thing the illuminati did as a group in the comics was to assemble the Infinity Gauntlet and try to use it. They wanted to will the gems out of existence, which was not gonna work. Predictably, when the first plan did not work, Reed Richards was still wearing the Infinity Gauntlet.
Just putting on that glove was a bad enough idea for Uatu to show up and tell Reed to stop being stupid. And putting on the glove is the first thing the Illuminati did as a team effort. Bad ideas across the board from those guys, and all borne of good intentions.
Maria Hill would not WANT to be a part of those shenanigans. But Maria would know she NEEDS to be there in order to keep them from getting worse.