Wouldn't have had my last three or more jobs if I were illegal, and those were key. I'd probably be turning a wrench at a lawnmower shop in Woodland living in a $550/mo hotel apartment and looking for things to steal in my spare time. Seems like an odd convo to pretend to keep everything the same in your life and then blink and pretend you're illegal from this point forward, as if there are any real life parallels. But, if the constraints must be the way they are, which intentionally excludes the biggest problems(work and travel), you can still get loans and whatnot, so I think that aside from all of the intentionally excluded downsides, then there aren't many downsides. Maybe some social issues since you'd hypothetically be claiming you're undocumented and there are no constraints on that, so we'll just assume you tell everyone you meet. Might get your ass kicked a few times.