I think you're partly describing nationalisation of a business when it becomes so big it can't be left alone and needs to be readjusted to help the market.

It's bought by the gov ("payout to the shareholders"), regulations are enacted to delimit what it can and can't do, and the whole thing is setup to make sure it's for the benefit of the larger public, with additional consideration on how to reintroduce competition on part of its mandate.

We' ve seen it with postal services and telecom, and if the whole thing becomes outdated it can spun out as a private entity again.