A new office building, named River Point Chicago, with an address of 444 W. Lake Street, will eventually be built on the site. The building is slated to rise 45 stories, with a height of around 650 feet, though the developer has indicated that it may be built taller, if needs dictate. They are currently building a platform over the tracks, which will serve as an elevated plaza, as well as a smallish riverwalk.
Further details, with plenty of renderings, are available at the following:
http://www.chicagoriverpoint.com/home.html