I too would like to see native Linux support in the future, but for the moment I have had good success with DD and Steam in Wine. It is a little messy, but I've played more than 100 hours with no game-braking issues, so I say it's fairly stable. Just say if you need help setting this up.
Is the plan to upgrade to Unity 4.0 before the eventual mobile release, or is 4.0 not a requirement for mobile? (I'm not very familiar with Unity)