Many of us would be aware of Desktop Notifications. Its something that would notify us when we are inactive, essentially with the message, when mentioned by someone.
How this would work:
1. A notification dialog box will pop up with the message at right corner of our screen if we are mentioned by someone, provided we are inactive.
2. It would also be great to filter the possible usernames as we try to mention someone. For example, in twitter we use @someone and it also does filtering as we type.
This might not be a good idea when people chat like they play bullet chess. But works when users are inactive and would not like to miss when someone mentions them.
However, the second point mentioned above, would put lot of load for filtering the usernames in rooms like cafe, where traffic is always high. This could be an optional feature allowing the user to mention the username correctly.
Finally, of course only VIP users can be allowed to enjoy this feature.