Basically the ability to use some keyboard shortcut, click, and have an extra caret to type at. Much like it does in Sublime, Atom, PHPStorm, etc.
Not sure what sort of insanity would have to go into implementing something like this system wide, but imagine how useful would this be. Have you ever been in a document, a website, etc, and thought how nice it’d be to quickly be able to type the same things in multiple places.
Just an idea!