Would be cool if this data coule be injected in the signal to a TV. Bring back Ceefax! :-D
In some countries it still exists though, which is pretty wild.
That's exactly what he did - if you look at this history section, he was broadcasting analogue TV signals to his house, and embedding his own Ceefax service in the signal!
888 should result in text on a transparent screen, whether or not there are subtitles available. Here it does nothing.