What is holding bitcoin SE back from becoming a fully accepted SE page? It's been in beta 1500+ days. Looking at the area51 page, it seems like it meets at least OK and above on the metrics. Are there specific requirements a SE site must meet before progressing from the beta stage?
There are a few reasons for that, but the #1 thing I want to emphasize is this:
90 days is a minimum length. Most sites will take much longer. Longer-running betas are not in some sort of failure mode, nor are they "trapped."
In fact, there are many sites that are still in Beta that are actually older than Bitcoin SE. http://stackexchange.com/sites#oldest
Site graduation out of beta represents a judgement by the StackExchange team that the site is self-sustaining and self-governing, and doesn't really need any further micromanagement to succeed. Several different things kick in at that point: moderator elections, a custom theme for the site, and a footer link to Bitcoin at the bottom of every StackExchange page. In terms of day-to-day operations, though, very little changes.
There is no hard-line test for graduation readiness. However, I can think of some factors that would undermine a request to graduate if we went for it right now:
There was a period of about a month about twenty two months back where no flags were being cleared, which meant that Community Managers (people paid by StackExchange) had to clear them for us. There's always some number of issues that need to be escalated to a CM, but bothering them with every spammer that comes on the site is not good.
We need more questions per day, but I think that's something that we're working toward organically.
So, gloom aside:
We're in a good position right now, because we have three engaged moderators, (Murch, Stephen, and myself) and questions consistently get good answers, from users like yourself, Bitcoin, Pieter Wiulle, and a whole bunch of others that I don't have space to thank. We've got consistent week-to-week pageviews, mostly referred from search engines, meaning that we already have a valuable reference.
So, I'm optimistic about our odds if we went for that down the line. ;) I'm actually interested in hearing about how other members of the community feel about graduation.
How sites are supposed to graduate:
In reality, 90 days is a minimum length a site is expected to to remain in beta. The blog post, When will my site graduate?, explains that a site can stay in beta as long as necessary to reach critical mass. As long as the questions represent real problems and consistently receive great answers, the site isn't going to get closed down. "It takes as long as it takes."
The Area 51 summary does not represent some sort of "report card" filled with pass/fail grades. If you're expecting someone to show up on the 90th days and say "Sorry, times up. It's time to go home," it doesn't really work that way.
Adding to Nick's answer:
A few months ago I've talked to our Community Manager contact about the requirements for exiting the beta. My understanding was that our site has been making a lot of good progress in the past year, but they're waiting for the activity to pick up some more for us to graduate from Beta.
From other threads on meta.stackexchange, I got the impression that consistently getting more than 10 questions daily is perhaps a lower boundary to get scheduled for exiting beta. More answers per question would also be a metric that could be better.
So, please help getting more good questions and answers on our site! :)