If it's been a little while since you last looked at Atom, then consider trying it again, they've spent some effort on optimising it lately. I mean, it's still not the speediest around, but it's improved leaps and bounds from even a few months ago. It is obviously not the only editor with an OmniSharp plugin. There are many others. [1]
I believe that debugging support on VS Code is currently limited to Node and Mono (and that's only on OS X/Linux) [2]. The team(s) behind OmniSharp (that is the various editor plugins) do desire bringing debugging support to one or more editors.
[1] http://www.omnisharp.net/#integrations [2] https://code.visualstudio.com/Docs/debugging#_common-questio...
To be honest, as long as VS Code is free-as-in-beer, has a plugin-in system that's flexible enough for the community to go nuts with, and can adequately serve as the primary development environment for an ASP.NET app... then I'm delighted.
However, perceptions mean a lot, and in the long-run I just don't see it getting uptake from the Python/Ruby/Node.js crowd without being open source. More of a marketing issue than anything else (although there's also the concern that MS could abandon it someday).