Previous reddit lasted 3 months tops before it degraded into a lot of nonsense. What makes you think that n.yc will last even that long before it gets flooded with crap?
The whole appeal of this site was that you could spend 10 min reading top few stories and you'd get a pretty good idea what's going on in the YC, VC, angel, investment community. Now we'll have to spend tens of minutes weeding through all kinds of topic that just waste your time.
Why not start a new website with this new theme? Since YC i a seed stage investment firm, what exactly does "Hacker News" have to do with YC focus and mantra focus?! It is a subdomain of an investment firm so the focus and direction of n.yc really makes very little sense.
Reddit held out longer than three months. I remember remarking to spez during Startup School '06 that I had noticed a recent, slight downtrend in quality. That was around the time that random photographs started appearing on the front page, and a couple weeks after the famous "Paul Graham Eats Breakfast" post. But it was far from nonsense then: the majority of front page content was still excellent. Reddit launched in late summer '05, so that's at least 8 months that it held out.
I don't know how it will turn out, but I think reddit worked out really well. It's no longer a hacker news site, but that's not really a bad thing. It's a great service for a lot of people. Honestly, the extistence of reddit and programming.reddit means a lot of people already have fine places to be.
news.yc and reddit are both young, even in internet time. New members are important, and any forum must adapt to stay relevant.
As for the word "hacker," there is no uncertainty about what it means among hackers themselves. And our sense of the word is spreading, not contracting. I saw a headline in the NYT a couple weeks ago that used "hack" in the good sense.