I'm writing an essay on what technology is missing for decentralized publishing of serial content (webcomics, fanfiction, podcasts, etc) and read-state synchronization is one of my topics. I'm hoping Microsub can be one good answer in that context.
For the kinds of serials that have ongoing plot/continuity, it's worth noting that
- entry order matters, and
- creators sometimes add or remove entries arbitrarily far back in the archive.
As a result, individual entry read-marks matter here because you'd like to know that there's something new even though it comes before entries you've already read.
Also: old entries can be edited. You may want to know that you read an older version of the entry so you can decide whether you care to read the updates, so I'd like to keep track of what the last-modified timestamp was for the version of the entry that you read. Note that this is not the same as the timestamp when you read the entry, because you might be racing with the publisher's updates.
I could picture it also being useful to record the timestamp when you read each entry for some kind of data analysis later—for example, predicting which feeds you like best, or clustering feeds that you like to read in close proximity to each other. But I don't think that's important for a first version of this spec.