Holger, your design has the same issue as every other HN app - it trades condensed view for spacing and typography. The brilliance of HN's native design is an ability to see 20-30 stories per screenful. This is a must have. Otherwise it turns into Designer News [1] :)
Secondly, an app that is merely an alternative view of HN webpage is not terribly interesting. It should really offer something else. For example, an ability to track/follow other users, ability to pick up stories from /new page that might of an interest to me, track my account stats, track replies to my comments and submissions, etc.
If you are going to sink your time in this project, make damn sure there'll be (paid) downloads at the end of the road.