The title has been changed here on HN and doesn't reflect the article:

  Unity 4 is also the first version of the engine to
  offer support for "the estimated 10 percent of the
  game-hungry PC market" that runs Linux, though the
  feature will only be available in "preview" form
  for the time being. Those that pre-order Unity 4
  starting today will get access to a beta test for
  the new engine, ahead of a full release that is
  still undated.
    -- from the article