I would think that each station already has a record of all their closed caption text. Are you saying that you would just like to have access to it all?
I believe you can already get the text in DVD's from the files on the disc.
I don't really watch enough TV to benefit from this.. What use would you put it to exactly?
If there were a transcripts of all the news stations, for example, then people could do basic comparisons of them. So they could say how many times FoxNEWS as opposed to CNN used the word "terrorists" or "nuclear strike." It would allow people to track advertising too, and just to get a general feel for how each channel carries themselves.