ehh, i thought over about it, it doesn't really work the way I thought.
Below is the idea:
Well, if we are implementing something like, 'Mark specific topics as read', users can put in topic ID in a field and every time the user logs in, a cron job is ran which would mark the topic as read if they are updated. But the bad thing is, if the topic gets updated after we login, it will then show up. There could be a way to mark it as read until they logout. (Maybe constant queries being ran in the background, but this will really burn the MySQL server into ashes) After they logout, the cron job will no longer run and the queries being ran in the background will stop.
The next time they login, the same cycle continues.