Extra field on Requests: Date last modification

I've searched for this request, did not find it however. I would like to have an extra field added to requests containing the date of last modification. And by modification I mean an edit to the request, or an incoming mail message for example. With this extra field I could sort my requests by this last modified date, so the requests that are most recently modified will appear on top of the list.

Sometimes users mail a reply to an old ticket, it is reopened and the reply is added, but because it is an old request it stays low on the list and does not catch my attention.

Thank you for your consideration of this request.