Want to add my support for this feature. At my job we are currently converting a MediaWiki instance to Discourse, in hopes that we can increase its use. The wiki is our knowledge base and has become very outdated. We’re hoping that by switching to a more modern, interactive platform like Discourse we can get more staff to add and update info. Having most categories default to wiki is key as we need everyone to be able to collaborate on articles without needing a moderator to wiki the topic each time.
I’d also love to see @Tom_Newsom’s idea that users go to the first post when there are no unread replies, but defaulting new topics to wiki is critical.