I hope xray[1] catches up. I prefer atom's UX-UI to any other editor but I agree that performance is still an issue. MS taking over Github doesn't seem to bring to a bright future. I really hope I'm wrong.
With xray focusing away from improving the editor experience and more on this new version control thing [1] for now, it doesn't seem like we'll be seeing a GitHub-provided alternative to Atom for some time.
[1] https://github.com/atom/xray