This is a big feature request, so I'm not suggesting an immediate implementation or conversion. For the future of SE however, I believe it solves some existing issues which might only grow bigger as the network keeps expanding. I wrote this originally as an answer to When will Stack Overflow become irrelevant?, but since it's more a request than an answer, I decided to post it as such.
The bottomline:
Questions should be able to show up on multiple SE sites, instead of just one.
Relating to the problems:
- "Which questions go on which SE site?"
- "Would a certain new community steal users from another?"
- "All these SE sites are becoming a mess, there should only be one."
The solution I believe, is to focus on users, and not the categorization. If enough C# developers feel it is useful to have a Q&A site for all C# questions, there is a reason for its existence and it could become a thriving/working community. If it has overlapping questions with other sites, that's what those questions literally should do, they should overlap, and appear on both sites. The advantage is you create a highly specialized group of experts, without interrupting any other SE sites.
Additionally this could have the following advantages:
- Resolve redundancy of tags. Tags could be filtered out on certain communities.
- Resolving ambiguity of tags and questions.
- Easier to determine whether something is on topic. (For users and moderators.)
- Specialized moderators. More moderators. (Overlapping questions can be moderated by moderators of multiple communities.)
- Separated (and shared) reputation. When proving your worth in one community it can also count towards reputation in another where the question is relevant.
- More accurate answers by reaching a more specific audience.
- Sub sites could start off with subsets of questions of other SE sites. You can compare it with the main Stack Exchange site at the moment. A favorite tagset is a candidate for a SE sub site.
A concrete example:
- Stack Overflow: specific programming problems
- Code Review: working code samples to be reviewed
- (fictional) C#
An expert only interested in C# questions can be active on C#.SE, while generalists can still stick around on Stack Overflow. A user with a specific programming problem could either end up at Stack Overflow, or C#.SE. The question would be visible on both. A user who wants a code review on C# code, either ends up at Code Review or C#.SE. The question would be visible on both.
Of course there are still plenty of details that would need to be filled in.
"How to know what sites a question belongs to?"
- Some tags become 'site' tags. E.g. C# for C#.SE.
- Only cross site moderators can make questions overlapping?
...
That's how I would like to see the SE network. Implementing it is a different story. :)
Some related discussion such a design would solve:
- The 'party problem' where people have nothing in common on a site as described in Stack Exchange podcast 2. This is one of the reasons why HowThingsWork didn't succeed. For people wanting to ask such a question it's a great place, but the community can't have knowledge about all those questions.
- Which meta am I supposed to post on? General meta questions could show up on the main meta and all child metas, while specific meta questions are only visible on the matching child meta.
- Overlapping stack exchange sites and rep migration when merging questions.
- Reputation could become more meaningful as a level of expertise, which when looking at meta is something a lot of people value.
I might update this list if I encounter others.