I guess corporates should take the lead and start moving their HQs out of Mumbai. The poulation gets diverted to other cities naturally. I don't think such a hue & cry is necessary at all.
Also, if the Govt so badly wants to decongest Mumbai, why doesn't it move all the Govt offices out of Mumbai, say Washi, Navi Mumbabai or so.. All the Govt employees will automatically move out of Mumbai. It's just lack of political will motivated by the landholdings of the politicians and the real estate barons. Dunno what poor Mr.Bachchan has to do with this.