Yep. In fact, I'm actively working on building something like that. Although I use Reddit as a comparison more than HN, and the scope goes further than a Reddit/HN clone, that's a big part of it.

If you're interested in looking at what I'm doing, it's all open source. See:

(project site):

http://code.google.com/p/neddick

(Github repo):

http://github.com/fogbeam/Neddick

(demo site):

http://spdemo.fogbeam.org:8080/neddick1/

(warning: the demo site can be abysmally slow at times, but I'm not promoting this real heavily yet, so I haven't put a lot of effort into make the demo real stable and performant.)

2. karma points (reward for being active and a way to find out what is more interesting - like on HN)

That and any notion of "gamification" is one thing I haven't done much with yet. I'm still undecided on the extent to which it has value in an organizational setting.

My approach is also less Quora like (I started before I discovered Quora, or maybe there would be more of a Quora influence), and is more like Reddit. But I'm working on another piece that I've been describing as a "sort of mini "Facebook" that will deal with managing social graph connections, and will have support of more of an "activity stream" type of thing.. I'm envisioning a very pub/sub model where you can subscribe to "things" you find interesting, whether that means "subscribe to this tag" or "subscribe to updates from this app" or "subscribe to status updates from this user," etc.