Re: the super-majority - it was my understanding that the super majority was imposed by the leadership of the house (Madigan - father of the anti-gun States Atty of Illinois Lisa Madigan) and possibly by the senate leadership - as it was a law that would effect home rule cities - (ironically state wide bans and taxes on firearms seem to not require such a super majority).
I would like to think that Rahm's rash proposal to tax and register handguns would cost democrats their seats and tip control of the senate and house - but didn't see that happen in the last midterm election - when you had the Dem. Governor removed from office due to criminal charges and replaced by his Lt. Governor - in fact Quin was elected governor - all that despite a nationwide tide that was running against Dem. candidates.
I believe if there are enough votes to pass CC legislation with a super majority then there would theoretically be enough votes to override the governor's veto.
However the vote counts on close legislation are suspect as often once there are enough votes to defeat passage of a bill - representatives whose votes aren't needed are allowed to vote whatever way will allow them to look good for the next election. Therefore not all those who voted for CC may be solid votes for it.