But isn't it true that the table should as well as include the user ids?
Because I didn't mean that the list needs update but rather the list will be the same list just providing addtionally the information to the logged-in user that if the question on the list is read by him/her or not. That's why I guess the table should include question id, user id, view-date (or a boolean?).
So, the plugin should only check whether THAT question has been viewed by THIS user or not.
By the way, the activity page becomes inpractical for a question that is not read many times ago. For example, if I have missed a question asked 3 months ago, it should always be in the list of "unread questions".