NeoVim can be trivially extended in any language. They're putting a lot of effort into making sure that the msgpack protocol supports basically everything. This means that, unlike in Emacs, it's straightforward to write extensions in whatever language is best for the job--something really, really important when it comes to language bindings themselves, which is probably the main thing I frequently find myself extending in Emacs in the first place. So saying it's written in a worse language seems bizarre to me.
NeoVim also, unlike Emacs, is cleanly split into a frontend and a backend so that its editing core can be used in different contexts. Combined with the above, that means you will eventually (hopefully) be able to get "the real" NeoVim in lots of apps, rather than either a kind of broken "Emacs mode" (like in IntelliJ, NetBeans, and Emacs) or having to do this weird "save a text blob to disk, open in Emacs, wait for it to be closed, reload in the app" dance. Already, this separation has allowed the creation of NyaoVim (https://github.com/rhysd/NyaoVim), a browser-based front-end that I could imagine being incredibly useful for remote editing, whether in a cloud-like environment (e.g. Cloud9, CodeAnywhere) or on a remote server.
Emacs is great. NeoVim is also heading in an excellent direction. You don't have to give it a chance, but you also don't need to be so dismissive.