I also have high hopes for NeoVim.
There is plugin called deoplete[1] that is doing asynchronous code completion. It shouldn't be too hard to connect it with OmniSharp.
For the last few months, I don't write C# any more, but still use emacs for F# development.
https://visualstudiogallery.msdn.microsoft.com/2beb9705-b568... http://www.hanselman.com/blog/SimultaneousEditingForVisualSt... https://visualstudiogallery.msdn.microsoft.com/f301cf82-e80b...
That's the kind of things that really set IDE vs editor in terms of usability.
Mostly I think it's just about preference. I like my editor lean [insert joke about emacs being bloated here], visually non-distracting and customizable. I also try to avoid using my mouse. Emacs is all of these things for me, VS is not.