I don't even know whether or not this is possible but is there any sort of website application or tool that maybe works in conjunction with a mod that refreshes a page with information regarding who's online in-game? Taking from the guild roster or your friends list?

Problems:
1. You need to Upload the data
2. You only can export data by reloading the UI or re-logging.
3. Auto-Upload needs to be triggered, either by checking if wow isnt running anymore or by last modified date changed of the saved var file.