Sorry to dig this up again, but the repetition of "Last reply" is really getting on my nerves. It's also less than ideal on mobile, because it pushes the important info (time/username) off of the screen in some instances.
I'd like to revisit the idea of removing the "Last reply" text altogether. As Toby mentioned, it could be confused with information about when the discussion was started. However, I feel like people will quickly catch on to what it actually represents (last activity), by virtue of the fact that the discussion list is ordered by it. I do like that it puts the time and the username front and centre, with no distractions. The important thing is that the username isn't immediately next to the avatar.
Anyway, to try it for yourself, paste this into your browser's URL bar and press enter:
javascript:app.translator.translations.core.discussion_replied = '{ago} by {username}';app.cache.discussionList.refresh();m.redraw()
You can try other variations by altering the {ago} by {username}
part – let me know what you think!