But these days it also makes sense to ask instead "why should I use Vim?" The version of Vim that you actually use probably wasn't installed by default on your main development system. So installing Nvim is the same as upgrading Vim.
From the nvim GitHub page:
Modern GUIs
API access from any language including clojure, lisp, go, haskell, lua, javascript, perl, python, ruby, rust.
Embedded, scriptable terminal emulator
Asynchronous job control
Shared data (shada) among multiple editor instances
XDG base directories support
Compatible with most Vim plugins, including Ruby and Python plugins.- It's ok if this person doesn't want to use Nvim.
- The "Why should I switch to Nvim" question is based on a questionable premise. I think the question should be "Why should I should to Vim".
And since Vim 8.0 does terminals and asynchronous jobs now, I don't see much value for Neovim unless you have an IDE that integrates Neovim via its API.
This will be the biggest win for Neovim. When something like pycharm/webstorm vim support is moved to real vim rather than a reimplementation I will change.
(And to be fair, switching on Arch is really easy since it's in the official repositories)