IMO for a site like this to succeed it needs to offer something HN doesn't. Chat, subforums, personal promotion section, something.
Depending on where you're reading, it's Hacker News that's a subset of just about anything else.
The things this site used to offer was there might be an article about a security breach, a brand new highly anticipated feature in a major product, a historical article about a long forgotten but major technological achievement.
Then a key person from that story would chime in with their take about what the article got right or wrong, offer to answer questions. And that is assuming they didn't directly make the post.
Nobody actually wants to read self promotion blog spam, besides other people pretending to be engaged so they can do the same
If HN is a subset of other sites (though arguably its approach to UX and moderation offer something different), a site targeting a subset of HN's users seems unlikely to get much traction.
But the invite only structure is limiting. I like the mentality behind it, but for so, so, so many of the communities I browse, the issue arises from size before any of the problem invite only solves.
And I don't need crazy frequent posts. Just something where I check after 2-3 days and it's not just 1 post with zero comments.