On Authonomy’s message-board a while ago, a writer commented that she thought that HarperCollins would probably find one manuscript on Authonomy each month that was good enough to publish.
One a year might be a more reasonable hope.
When I was an editor I’d have been thrilled to find one publishable submission a month. But the vast majority of submissions I received weren't even readable, let alone publishable. Perhaps 10% were coherently written and showed a reasonable understanding of spelling, grammar and punctuation: but we considered very little of that 10% for publication because most of it just wasn’t suitable for our lists. We published non-fiction but fiction made up about half of the submissions we received; and the non-fiction that was submitted rarely fitted into the genres we worked within.
Based on what little I’ve read on Authonomy I’d say that a lot of the writing showcased there would come in the top 10%, so is already ahead of the game. But most of it is still a fair distance away from being publishable, as is perhaps evidenced by the fact that so far, just one book has been picked up for publication from the many that appear there.