Add a "Last Chapter Read" Feature

[balthanon]

One of the biggest features that I think would improve Ao3 is a "last chapter read" feature for the site. My preferred location to read fanfics anymore is actually Spacebattles or Sufficient Velocity primarily because they automatically track which chapters of a fic I have read and which I haven't. I don't need to remember to bookmark a page or update that bookmark later. I've suggested it and even attempted to volunteer my time to build it, but it sounds like it isn't something they're interested in at the moment, so I was thinking about developing a user script or extension myself when I ran across yours.

It's likely significantly more work to do it outside of Ao3, but given that you've already worked with the site a lot, I thought I would at least suggest this as a possible new feature to add to your toolset.