Summary

Add ability to mark topics unread. Furthermore, maybe within the same step, allow individual posts to be marked as unread.

Reason

It happens a lot that you read a topic with important information but only have the time to skim over it. You want to read it fully at a later time. Subscribing to the topic only gives you the ability to see when a new reply has been made. You could add it to your bookmarks, but this assumes you remember you bookmarked a topic and visit the appropriate page later. With the ability to mark it unread you are able to see it instantly the next time you log in.

Variations

A variation of this feature would be to add a new topic type similar to dotted topics to mark topics important for the user - but this would be rather the bookmark feature evolved.

Implementation

Currently, iirc, there is a Mod doing this. The implementation would require changes to the unread tracking system, database changes would be not required.