It seems as if the HN infrastructure hasn't been updated in a long time and is really slow for submitting or commenting on stories. Is is time to switch HN to a different platform?
Yeah... It is somewhat slow. And for some question, I was trying to comment, but it just wouldn't let me for some reason. It just kept me redirecting to some "/r" page. I logged-out, logged back in, but still had the same problem. But it worked after someone else had made a comment.
HN is (roughly) open source: https://github.com/nex3/arc/blob/master/news.arc although it doesn't necessarily correspond to the currently running version. You can do the facelift yourself via any number of Stylish userscripts.
Reddit's source code is going to be relatively specialized for their architecture (Cassandra and EC2 and whatever else), and piggybacking on a subreddit is going to encourage bleed, lower control (e.g. pg restricting signups at times), and change the value of karma to represent a cross-culture value instead of what's valued locally.
What advantages are there for merging? You save one password?
If you look at the numbers though, there were several times in the past when HN was slower than it is now.