I don't know.. There is something wierd about "encouraging engagement" when users are not looking to engage. Not everyone is an author. Constantly remind them that they are there to post by making such a prominent button available can be seen as very annoying. 

Besides, I don't think moving the button to the top is that "discouraging". 

 Exactly! 
Note also that there will be other and way better apps for instant post writing and publishing. (Shipyard being just the first)
Encouraging engagement is more about making it super easy and fluid to comment, join chats and community and discover like minded folk.