That's an interesting system and group of thought types. I have something relatively similar, although it's modified a bit more towards my own uses of PB and set of responsibilities.
I think the problem of making and maintaining "common brains" is one of perspective. Mainly, everyone has a different one. Common brains will work when it's created for a specific purpose, by a group of people with the same perspective on that purpose (as shown in by a corporate EKP solution). This allows a common language, everyone can agree on definitions, types and knowledge base structures. However, once you step outside this artificial constraint into a public realm, the difficulty of creating a database that's understandable to everyone grows exponentially. This is why keyword search engines are so popular, and why tagging is mainly a personal solution. A lot of money is being invested in creating a semantic web, but the amount of information and the differences people have in categorizing it makes it a very difficult process, both to implement and get adoption. Which brings me back to the list of types, which sort of exemplifies the problem. While I have some similar ones, I've had to customize my own for something that makes sense to me. For me to try and fit my data into the tags it creating an artificial restriction, and increases the time it will take to get data into my database and find it. This will increase my frustration, so I'll end up either not using it at all, or customizing it within a month. Some people don't even use types, so it wouldn't work at all for their usage. I've found that implementing an organization style for myself it a lot of putting stuff in, arranging and re-arranging into something that makes sense, watching my habits, and reading or seeing what others are doing. Even when seeing what others do, I don't implement that exact system. I generally think on it for a few days and incorporate a piece or two into my system and see what works. I have to make it my own. And that's really what I think the crux of the issue is with common databases. You have to either make it your own to understand it, already have a common perspective around it, or spend a lot of time figuring enough about the layout and information style to internalize it and make it useful to you. Sorry, this doesn't really help going towards a common brain, or the requirements to do it, it's just more of an opinion around the challenges around it, and that different situations or databases will have different requirements specific to the problem you are trying to solve. Whew! P.S. Where did a 19 class of data restriction come from?