I'been using WordPress since 2005 and although I'm pretty much conquered in all respects, I still wonder how some possibilities are not there for the user.
One of them: changing the default TinyMCE editor and replacing it with other modern alternatives. The popularity growth of the Markup language is clear, and the new Ghost CMS makes a point in this respect. Why does WordPress not support this fully either natively or with an official plugin?
I will go even further: I'd like to use whatever editor I want. In my case, the Medium editor is absolutelly stunning, and I'd be delighted to be able to combine that editor to the other WordPress features.