This is a bit late.. but a lot of PKM-scene are using bookmarkers and readers with offline webpage saving and search already. I suppose this is enough support as a lot of scene seems more interested in optimizing the information organization tooling experience that comes with the separate apps and bookmarking formats.

I think these sorts of automated personal knowledge gathering systems are an under developed concept. There is things going on though with projects like Spyglass which does local website indexing and search.