I don't think it is a retractable roof they would be considering. But how about a glass ceiling with glass that is either clear or opaque (changable) depending on the time of day and event needs? Something like this technology (smart glass):
http://en.wikipedia.org/wiki/Smart_glass
Just a thought. Be cool for a blimp over a game at night to be able to look into the arena and see the action, much like a football.
And I think they are likely thinking of something like AT&T park where folks can watch some of the game without paying for tickets (stand outside and look in) but with removable glass barriers so they can open them and extend the "fun" to those outside.
Just a couple thoughts. Wonder if they are anything close to what they are coming up with.