We linkify text submissions for Show HNs and other interesting text posts where it's clear that the feature isn't being misused. I did that on the OP.

See also https://news.ycombinator.com/newsfaq.html:

Q: How do I make a link in a text submission?

A: You can't. This is to prevent people from submitting a link with their comments in a privileged position at the top of the page. If you want to submit a link with comments, just submit it, then add a regular comment.