On most MCC owned property you are allowed to smoke, it is up to who rents or leases it what they do unless it is against the law. City have a 250 year ease so as good as own it.I agree with the cage idea but as the stadium is owned by Manchester City Council, it will never happen. The council has a pretty inflexible attitude to smoking on any premises that it owns and would have the final say. Even if City were in favour, the council would never approve of any designated smoking area(s) within the stadium.
I smoked until a few years ago and it never entered my head to light up inside a football ground once it was banned. If you can do without it on a flight that lasts 2-3 hours, you can manage for less time than that at a game.
Anyone could smoke at CoMS when it opened.