Actually the 2nd boutique hotel operators has already been announced. It will be run by the The Light Group. They are not currently hotel operators but they operate very trendy nightclubs/restaurants (Light nightclub and Fix at Bellagio come to mind).

In addition to these two boutique hotels, MGM Mirage will operate their own 60-story, 4000 room hotel on site. They will have 500,000 square feet of retail space and two 500-room condominium high-rises.

It's going to be quite impressive once the whole project is completed. The whole project is supposed to cost over $5 billion dollars.