I used a plugin to add this functionality for a long time, so thanks for bringing it into the core plugin.
One note on usability, something I found slightly off in the new implementation: when selecting a link from your list of posts, the “link text” field remains empty. The user has to remember to also fill in the link text, which in many cases will be the same as the post title.
Here’s a quick screen recording of what I’m talking about: https://gfycat.com/BlandPalatableAmericanwigeon
Can I suggest that you fill the link text with the post title as a default, while allowing a user to easily change that if necessary?
