In fact Atlassian have a module for this that plugs into Confluence which looks and feels a lot like SO. Trying to find the module name. It might just be called "Questions". I think this is the one we use [1]

[1] - https://marketplace.atlassian.com/apps/1217080/questions-ans...

that'll only work if the module name also makes confluence search usable

Yes, their search leaves a lot of room for improvement. I am only suggesting it for the folks that are already using it.