It’s a good question and I do have another idea that would fit well within Readerkit so I am going to tell it to you now.
On MLKSHK, the site my wife and I created a few years back, there is a little banner that shows up between posts where you last started reading:
It is created when you first view your incoming stream and displays the timesince it was created:
You can use it to “jump” back to where you previously started and work yourway forward.
It is an automatically generated bookmark that is inserted in between posts so you can determine where you last left off reading so you can be sure to catch up with every post.
I could see the initial sell to readers would be: “sign-up and get this handy bookmark generated for you”.
Readerkit could also send out a monthly “Here are posts you might not haveseen” along with the bill described in my last post.
So there are two ideas for you.