"Bom Bahia" is a false popular etymology. Bom is a masculine form; you'd expect Bahia Boa if anything. The name predates colonialism and--not surprisingly--had several competing variants: Mumbai, Mambai, Bambai, etc. The first is now the preferred Marathi version, but less than half of all Bombayites (or, if you prefer, Mumbaikar) have it as their mother tongue, even if it is the official language. A majority speak Bambaiya Hindi (http://en.wikipedia.org/wiki/Bambaiya_Hindi), and the Hindi version is Bambai and has been for hundreds of years. Why should this suddenly change based on the whims of the Maharashtrian nationalists? It's like declaring that the official name of Chicago should henceforth be "Chicawguh" and that everyone worldwide should change their transcriptions accordingly.