My biggest gripe with this is that if I want the post I am writing to look good then I want both the link and a title to go with it. So to make this easier there are two options, as I see it:
When you click the “Insert Hyperlink” toolbar button and paste the url then Discourse will detect if the link is to something in Discourse and then looks up the title for it and copies it into the “optional title” field.
When rendering a post to the screen, when discourse finds a link (without a title) then it checks if this is a topic, category, etc and then gets the target title and decorates the rendering accordingly.
I would myself prefer option 2, but maybe in the Insert hyperlink box there could be a help-icon that pops up an explanation about how internal links are decorated?