Consumers are going to get their Blu-ray expanded.
"This feature allows for a second video source to lay on top of the main film. This can be used for various special features including video commentaries and 'making of' pieces."
What makes the Sunshine Blu-ray disc release different, is that it "will be the first to do it with two separate streams on Blu-ray (this had initially been done by creating an entire new video with the second video stream hard encoded into the other). However, this method is only compatible with profile 1.1 players. None, is currently available on the market but Samsung's upcoming $1000 Duo player will support this and it is believed that the Playstation 3 console will be able to support it in the future. Regular blu-ray players sold so far will not be upgradeable."
Interestingly, HD-DVD players have always allowed for this feature. Fox also has plans to put 100 Blu-ray titles next year.