I have posted a similar concept few days ago.
The result? I got a "fuck off" by the Leader Maximus.
It was your approach. Jon probably read it as you saying what will happen, I know I did as I was skimming through that thread a few days ago.
The point is, we've tried a private forum. It died off because people lost interest. Part of what makes Wickedfire great is that all of the information is free and open for people to offer their perspective.
Am I saying that there shouldn't be a restriction on who can view that free information? No. I think, and as far as I know, just about every thread other than in STS require you to log in to view. If not, I know some are because I have gotten logged out a few times and had to log in to view the thread.
Now, I do think that there needs to be some restrictions on joining to make it so that it's not as easy as it is to create an account. Some have suggested a quiz, others have suggested an invite, etc.
An invite might work, but it'd also keep some people away who otherwise would have become amazing members of this community, simply because they didn't know anyone initially. A quiz would certainly ensure idiots at least looked at some important stickies, so maybe that's a better option.
I do think that there needs to be restrictions on posting until people have read some rules and stickies. It'd solve a lot of the redundant threads popping up, and I especially think we need them for SBT; for instance, only people who've made 100+ posts with 100-200+ words or more in them can start threads in SBT, so we know that they at least have made an effort to contribute to the forum and not just made a new account or spammed their way into it.