For a long time I kicked around the idea of a browser extension that archives the full text of any long webpages you spend more than 30 seconds on, for full text indexing and search.
Oh wow, this is exactly what I want, but with a server component so it works on mobile too (where I do most of my reading) and gets data from all of my workstations (I have 4-6 at any given time).
This would be that, but even better.