Don't see a point in that and to do it you would need a crawler of some sort
Yes. I also never saw the point in that (Don't even know why I had this idea, XD).
But making a crawler may have a point. Some think to download a site, or part of the site. Or just search in it in case that site doesn't have a search engine of it's own.
A more practical application would be some project to calculate various statistics on many different websites, like news sites, forums, social networks, etc.
But I don't know, just brainstorming, lol.