Cannot sort posts by the latest comment time

HI Team, 

I have to say that I'm tired of complaining about this very simple but should be a must-to-have feature, which is, to sort all my posts by the latest comment time by XXX. There are hundreds of posts made every day and how to make it clear on which post/comment has been submitted for a long time but never get replied? So far I only have 4 options,newest post, recent activity, Votes, Comment, nothing I can see with the most important field "By last comment time". 

With this feature, agents are able to manage to handle the post that needs to be replied in time, they can also know who is the last comment on the post, if it's another agent, they can skip that cuz the customer obviously did not reply to us yet. Save our time for workflow, and we don't have to check every single post to see if we need to make a new comment. 

Please fix it asap!!!