If you're going to try this, then it probably has to integrate with the en:Wikipedia:Reference desk somehow.
Topic on Talk:User Interaction Consultation/EXAMPLE: Q&A
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Perhaps the WMF could just run a Stackoverflow instance, with the questions somehow "attached" to an article. Maybe run it on a separate domain to avoid WP:NOTFORUM complaints?
See T31923 about a separate Q&A site.