They have already done something like this before. For games like Legasista and Mugen Souls, the companies were hesitating whether or not they would allow localization, but after so many people from NISAmerica wanted it so badly, they contacted their publishers and the games were scheduled for localization.
As said before from another user in this topic, it's not very likely, but it's definitely not impossible. The iDOLM@STER already has tons of support in America, and there's a lot of people who want it. It was also pretty obvious that most people who want the game already own the Japanese copy, but there are people who don't have the funds to pay for the game.
I forgot who said it, but yes, the game would be really expensive because of licensing, the music production, etc.