I've been thinking about early Cerberus back in ME1 apparently being an Alliance black ops unit as it was briefly mentioned before the next two games changed that entirely. I've been hung up on whether it'd make for a more interesting plot if Cerberus stayed as a covert branch of the Alliance, becuz that might mean there'd be an Alliance villain we'd have to face, but Idk if that'd be a can of worms 2010s era Bioware would be willing to open, since they were more concerned w/ the rule of cool kind of storytelling mostly.
They'd probably also be a fitting parallel to the Special Intervention unit, a branch of the Batarian Hegemony namedropped a few times in the trilogy, as I'd also probably use them in place of the Collectors in ME2 ideally. :v But Idk.. would anyone else see potential in either of these ideas?
I definitely see potential in Cerberus being fully a part of the Alliance - hell, if anything, Cerberus being Alliance-originating would give Shepard more reason to work with them in ME2, believing that they're a part of the same organization that they signed on with, giving them reason to believe that they're genuinely an organization on the same side.
But I agree, I don't really think 2010s BioWare would have gone in to that can of worms - both between running on a rule of cool and because at that time, I don't think that this was a time when implying that the good guys were in some way also the bad guys, or connected to the bad guys like that. There WAS, believe it or not, a more innocent time, even if it seems like it was forever ago.
A lot of ME2 could be tightened up by this sort of revamp - in addition to already being an organization Shepard would have some level of default trust in, it would also be a way of, in essence, Shepard getting to "clean house" of the Alliance prior to ME3 and the Reaper invasion, clear out some of the elements of the Alliance who would actively stand against the efforts of working with the Citadel races to defeat the Reapers. Given what we know of human nature... There's probably a good number of Alliance officers who could be convinced that a pro-human stance is a good idea. And once you get to that point, that leads to a tipping point of them being able to be convinced that Cerberus is a good thing.
That would be the kind of thing that averts the bridge syndrome I've said ME2 suffers from, the spinning of wheels in the waiting for the plot payoff in ME3, because it's characters trying to ease things before the invasion, rather than dealing with some separate-but-related threat.
That, ultimately, I think is what would really have served ME2 in its writing, to be about laying groundwork to build up a galaxy-spanning network, of Citadel races and non, to stand against the Reapers. It would be about exploring more of these groups and species, making that the core of the narrative, rather than try and come up with some side story that kept the Reapers in the background.