"Unread" on its own isn't always useful.

I watch close to 100 channels. Many of the channels are in a permanent unread state because they're not critical. What I'd really like to know is which channels have recent activity (say within the last hour) so I can jump into an active conversation.

This doesn't replace "Unread", but would be an elevated state, like "Hot Unread". After a period of time, it then falls back to "Unread"