The US never used Teletext, but we do have closed captioning, which should be recoverable and would provide some machine-processable date. Much less than Teletext would, though, for sure.
It's funny you should mention this - it's exactly what is on my mind at the moment too. I'm trying to resist the temptation to trawl ebay for peoples old VHS collections (search "used VHS" gives good results) and start building an archive.
Pity there doesn't yet seem to be any centralized effort to this though. I can imagine a wayback machine-like archive being an amazing resource.