This feature is actually already present on some screenings. For example this weekend's FA cup final allowed for selection of regular commentary or the Five Live audio stream, commentary from the BBC's national sports radio station. In addition, after the game users could watch highlights all weekend by pressing the red button on their remote.
Williams mentioned people can give feedback at the Points of View website as to ideas and comments relating to the technology.
As well as for the cup final, the BBC also offer a teletext/internet style service on the latest cricket score for the current Test match England vs West Indies. This is constantly updated and has pages much like the teletext pages which scroll through but is more advanced, providing latest photography and news of the event as it happens. Layered over the top is a live radio commentary stream.
Teletext regular service