I do want to see the code for this, not that I'm planning to blatantly copy, but sometimes it's good to take the best ideas and run with it and improve. That system sounds great. The nbb team have worked with drupal many years ago and I don't recall that spam detection code, must be new?
It's actually a custom system I put together using Flags, Userpoints, and Rules. I'd be more than happy to share the code except for there isn't any. It was all point-n-click created in the interfaces of those three modules. And just as well, because I'm a pretty bad coder. That's definitely a nice perk about using Drupal, it's extremely flexible and relatively easy for non-coders to tweak to their needs. But @psychobunny if you want to copy the idea in NodeBB please feel free and go right ahead, that's why I made this post.
I'd add one more criteria, if a post is accepted communally as spam, you get your flag quota back (because that validates your original flag)
#6 Users that have been registered for longer than Y days can not be locked out.
"&& have published n number of non-spam posts."
Adding that condition might solve the problem pointed out by @psychobunny here.
Also a great idea.
Let me know if you have any other questions! Thanks for all the replies and interest.