You can already add new posts to your event feed via RSS so no need to implement this again (on the other hand it would be better if those were opened in the app instead of browser - now that I think about it maybe you can hijack tmo links like ovi store hijacks ovi links)

Both subscribed threads and active topics is a good idea for the event feed, but I don't know for sure when they should pop up.

Active topics is more difficult to implement, as it's not clear when a new entry should be created. One solution would be to pop up any topic that wasn't into active topics and it appears on them, but then you will have the same thread appear again and again on the feed every time it is pushed out of AT and back in.

Subscribed threads are cleaner to incorporate. Any new posts in any subscribed thread would pop up directly to the event feed.