Say you are the owner of example.com with a wiki at www.example.com/wiki Say you decide to move the wiki to it's own subdomain: wiki.example.com/wiki. Would there necessarily be any "hit" on SEO assuming you implement permanent redirects at the www site?
Yes, there would be. That article still has validity. The basic issue is that if you have built up "momentum" and a bit of a reputation with Google, meaning DA or PA or other weighting factors, then when you (A) remove content from example.com you are asking for them to lower your ratings because now that domain has less information and (B) you are starting off essentially at zero rating for wiki.example.com, meaning you are starting off almost from scratch.
The search engines consider example.com and wiki.example.com as related, but essentially separate entities, which while not always what we want, is essentially valid and correct as for other sites, these are indeed somewhat independent entities.
Hope that helps.
Hershel