"Post New Thread" button outside of forums

The competition between forums and other social media like Twitter or Facebook is hard today. Therefore I think a forum should make it users as easy as possible to write new threads. It should also be possible from outside of a forum - for example from the community overview page.

Threads created outside of a forum would be place in a defined default forum - and moderator would then at a later stage move the thread into the right forum or subforum.

Now my question: How could I do that (have a "Post New Thread" button outside of a forum and linked to a defined default forum)?

Thanks for your help!