YES! We are going to update the Beta until we stop calling it a beta. You will still be the proud owner of a full license of the game. Everyone who backs our Kickstarter at at the least the first reward has a version of the final game.
Unity already supports MacOsX and Windows. The next version of Unity plans to support Linux, so hopefully it will work on that too even though we cannot confirm yet. We do not plan on supporting tablet and mobile platforms in the near future due to system requirements, so iPad and Ouya won't be supported until further notice.