There's a pull request on the neovim / neovim project that adds libvterm. This library is a C implementation of a terminal emulator that provides callbacks for drawing, so Thiago de Arruda has hooked into it and displays the output from within Neovim.
That means you can get a full terminal by typing
:terminal. It's even capable of running Emacs. There's even a video of this on YouTube: take a look at Emacs running in Neovim by Justin M. Keyes.
I found this on reddit/r/vim under Emacs running in Neovim. Besides the obvious Emacs/Vim jokes, people seemed genuinely impressed. If this ships in Neovim it'll mean we have to completely rewrite all of our "Vim as an IDE" posts!