You seem to oddly out of the loop here. Atom has been released for Mac only (private beta that too.) Linux, Windows builds are coming up, by their own admission. (My source? IRC and Discuss from atom.io footer.)
Besides, for the tech purported to be behind Atom: node-webkit, There would be no additional costs or efforts required to get it running on Linux.
If it is, as it appears, node + node-webkit, it might not be all that hard to build a web version, particularly one for Chrome/ChromeOS, since it would mostly be an app written to run on the same JS engine used in Chrome that already uses Chromium for its UI.